diff --git a/apis/python/src/tiledbsoma/_util.py b/apis/python/src/tiledbsoma/_util.py
index d2ea2db55e..3c2498c8a6 100644
--- a/apis/python/src/tiledbsoma/_util.py
+++ b/apis/python/src/tiledbsoma/_util.py
@@ -10,6 +10,7 @@
 from itertools import zip_longest
 from typing import Any, Optional, Tuple, Type, TypeVar
 
+import pandas as pd
 import pyarrow as pa
 import somacore
 from somacore import options
@@ -284,3 +285,29 @@ def pa_types_is_string_or_bytes(dtype: pa.DataType) -> bool:
         or pa.types.is_string(dtype)
         or pa.types.is_binary(dtype)
     )
+
+
+def anndata_dataframe_unmodified(old: pd.DataFrame, new: pd.DataFrame) -> bool:
+    """
+    Checks that we didn't mutate the object while ingesting. Intended for unit tests.
+    """
+    try:
+        return (old == new).all().all()
+    except ValueError:
+        # Can be thrown when columns don't match -- which is what we check for
+        return False
+
+
+def anndata_dataframe_unmodified_nan_safe(old: pd.DataFrame, new: pd.DataFrame) -> bool:
+    """
+    Same as anndata_dataframe_unmodified, except it works with NaN data.
+    A key property of NaN is it's not equal to itself: x != x.
+    """
+
+    if old.index.name != new.index.name:
+        return False
+    if len(old) != len(new):
+        return False
+    if any(old.keys() != new.keys()):
+        return False
+    return True
diff --git a/apis/python/src/tiledbsoma/io/_registration/signatures.py b/apis/python/src/tiledbsoma/io/_registration/signatures.py
index d8ea978690..3e88c230c2 100644
--- a/apis/python/src/tiledbsoma/io/_registration/signatures.py
+++ b/apis/python/src/tiledbsoma/io/_registration/signatures.py
@@ -67,7 +67,7 @@ def _string_dict_from_pandas_dataframe(
     allow the same.
     """
 
-    df = df.head(1)  # since reset_index can be expensive on full data
+    df = df.head(1).copy()  # since reset_index can be expensive on full data
     if df.index.name is None or df.index.name == "index":
         df.reset_index(inplace=True)
         if default_index_name in df:
diff --git a/apis/python/src/tiledbsoma/io/conversions.py b/apis/python/src/tiledbsoma/io/conversions.py
index f4f972fc1f..6de5007557 100644
--- a/apis/python/src/tiledbsoma/io/conversions.py
+++ b/apis/python/src/tiledbsoma/io/conversions.py
@@ -31,7 +31,7 @@ def decategoricalize_obs_or_var(obs_or_var: pd.DataFrame) -> pd.DataFrame:
             },
         )
     else:
-        return obs_or_var
+        return obs_or_var.copy()
 
 
 @typeguard_ignore
diff --git a/apis/python/src/tiledbsoma/io/ingest.py b/apis/python/src/tiledbsoma/io/ingest.py
index 428f6e4ef0..e5f4ed6fa9 100644
--- a/apis/python/src/tiledbsoma/io/ingest.py
+++ b/apis/python/src/tiledbsoma/io/ingest.py
@@ -1204,10 +1204,16 @@ def _write_dataframe(
     context: Optional[SOMATileDBContext] = None,
     axis_mapping: AxisIDMapping,
 ) -> DataFrame:
-    # The id_column_name is for disambiguating rows in append mode;
-    # it may or may not be an index name in the input AnnData obs/var.
-    #
-    # The original_index_name is the index name in the AnnData obs/var.
+    """
+    The id_column_name is for disambiguating rows in append mode;
+    it may or may not be an index name in the input AnnData obs/var.
+
+    The original_index_name is the index name in the AnnData obs/var.
+
+    This helper mutates the input dataframe, for parsimony of memory usage.
+    The caller should have copied anything pointing to a user-provided
+    adata.obs, adata.var, etc.
+    """
     original_index_name = None
     if df.index is not None and df.index.name is not None and df.index.name != "index":
         original_index_name = df.index.name
@@ -1540,6 +1546,9 @@ def _update_dataframe(
     """
     See ``update_obs`` and ``update_var``. This is common helper code shared by both.
     """
+    new_data = (
+        new_data.copy()
+    )  # Further operations are in-place for parsimony of memory usage
     if sdf.closed or sdf.mode != "w":
         raise SOMAError(f"DataFrame must be open for write: {sdf.uri}")
     old_sig = signatures._string_dict_from_arrow_schema(sdf.schema)
diff --git a/apis/python/tests/test_basic_anndata_io.py b/apis/python/tests/test_basic_anndata_io.py
index 2a8db5ad44..3df0b08e7a 100644
--- a/apis/python/tests/test_basic_anndata_io.py
+++ b/apis/python/tests/test_basic_anndata_io.py
@@ -15,6 +15,10 @@
 import tiledbsoma
 import tiledbsoma.io
 from tiledbsoma import _constants, _factory
+from tiledbsoma._util import (
+    anndata_dataframe_unmodified,
+    anndata_dataframe_unmodified_nan_safe,
+)
 
 HERE = Path(__file__).parent
 
@@ -109,6 +113,7 @@ def adata(h5ad_file):
     [tiledbsoma.SparseNDArray, tiledbsoma.DenseNDArray],
 )
 def test_import_anndata(adata, ingest_modes, X_kind):
+    original = adata.copy()
     adata = adata.copy()
 
     have_ingested = False
@@ -133,6 +138,9 @@ def test_import_anndata(adata, ingest_modes, X_kind):
         if ingest_mode != "schema_only":
             have_ingested = True
 
+        assert anndata_dataframe_unmodified(original.obs, adata.obs)
+        assert anndata_dataframe_unmodified(original.var, adata.var)
+
         exp = tiledbsoma.Experiment.open(uri)
 
         assert exp.metadata[metakey] == "SOMAExperiment"
@@ -411,13 +419,17 @@ def test_ingest_relative(h5ad_file_extended, use_relative_uri):
 def test_ingest_uns(tmp_path: pathlib.Path, h5ad_file_extended, ingest_uns_keys):
     tmp_uri = tmp_path.as_uri()
     original = anndata.read(h5ad_file_extended)
+    adata = anndata.read(h5ad_file_extended)
     uri = tiledbsoma.io.from_anndata(
         tmp_uri,
-        original,
+        adata,
         measurement_name="hello",
         uns_keys=ingest_uns_keys,
     )
 
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
+
     with tiledbsoma.Experiment.open(uri) as exp:
         uns = exp.ms["hello"]["uns"]
         assert isinstance(uns, tiledbsoma.Collection)
@@ -446,7 +458,7 @@ def test_ingest_uns(tmp_path: pathlib.Path, h5ad_file_extended, ingest_uns_keys)
             assert isinstance(random_state, tiledbsoma.DenseNDArray)
             assert np.array_equal(random_state.read().to_numpy(), np.array([0]))
             got_pca_variance = uns["pca"]["variance"].read().to_numpy()
-            assert np.array_equal(got_pca_variance, original.uns["pca"]["variance"])
+            assert np.array_equal(got_pca_variance, adata.uns["pca"]["variance"])
         else:
             assert set(uns) == set(ingest_uns_keys)
 
@@ -481,7 +493,13 @@ def test_add_matrix_to_collection(adata):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
 
+    original = adata.copy()
+
     uri = tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
+
     exp = tiledbsoma.Experiment.open(uri)
     with _factory.open(output_path) as exp_r:
         assert list(exp_r.ms["RNA"].X.keys()) == ["data"]
@@ -602,8 +620,13 @@ def add_matrix_to_collection(
 
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
 
     uri = tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
+
     exp = tiledbsoma.Experiment.open(uri)
     with _factory.open(output_path) as exp_r:
         assert list(exp_r.ms["RNA"].X.keys()) == ["data"]
@@ -656,8 +679,13 @@ def test_export_anndata(adata):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
 
+    original = adata.copy()
+
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
 
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
+
     with _factory.open(output_path) as exp:
         with pytest.raises(ValueError):
             tiledbsoma.io.to_anndata(
@@ -700,9 +728,14 @@ def test_null_obs(adata, tmp_path: Path):
     #   Create column of partially-null values
     rng = np.random.RandomState(seed)
     adata.obs["empty_partial"] = rng.choice((np.NaN, 1.0), adata.n_obs, True)
+
+    original = adata.copy()
     uri = tiledbsoma.io.from_anndata(
         output_path, adata, "RNA", ingest_mode="write", X_kind=tiledbsoma.SparseNDArray
     )
+    assert anndata_dataframe_unmodified_nan_safe(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified_nan_safe(original.var, adata.var)
+
     exp = tiledbsoma.Experiment.open(uri)
     with tiledb.open(exp.obs.uri, "r") as obs:
         #   Explicitly check columns created above
@@ -717,6 +750,7 @@ def test_null_obs(adata, tmp_path: Path):
 
 def test_export_obsm_with_holes(h5ad_file_with_obsm_holes, tmp_path):
     adata = anndata.read_h5ad(h5ad_file_with_obsm_holes.as_posix())
+    original = adata.copy()
     assert 1 == 1
 
     # This data file is prepared such that obsm["X_pca"] has shape (2638, 50)
@@ -728,6 +762,9 @@ def test_export_obsm_with_holes(h5ad_file_with_obsm_holes, tmp_path):
     output_path = tmp_path.as_posix()
     tiledbsoma.io.from_anndata(output_path, adata, "RNA")
 
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
+
     exp = tiledbsoma.Experiment.open(output_path)
 
     # Verify the bounding box on the SOMA SparseNDArray
@@ -860,6 +897,7 @@ def test_id_names(tmp_path, obs_id_name, var_id_name, indexify_obs, indexify_var
                 X[i, j] = 100 + 10 * i + j
 
     adata = anndata.AnnData(X=X, obs=obs, var=var, dtype=X.dtype)
+    original = adata.copy()
 
     uri = tmp_path.as_posix()
 
@@ -871,6 +909,8 @@ def test_id_names(tmp_path, obs_id_name, var_id_name, indexify_obs, indexify_var
         obs_id_name=obs_id_name,
         var_id_name=var_id_name,
     )
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(uri) as exp:
         assert obs_id_name in exp.obs.keys()
@@ -950,10 +990,13 @@ def test_uns_io(tmp_path, outgest_uns_keys):
         uns=uns,
         dtype=X.dtype,
     )
+    original = adata.copy()
 
     soma_uri = tmp_path.as_posix()
 
     tiledbsoma.io.from_anndata(soma_uri, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(soma_uri) as exp:
         bdata = tiledbsoma.io.to_anndata(
@@ -1002,7 +1045,10 @@ def test_string_nan_columns(tmp_path, adata, write_index):
 
     # Step 2
     uri = tmp_path.as_posix()
+    original = adata.copy()
     tiledbsoma.io.from_anndata(uri, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified_nan_safe(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified_nan_safe(original.var, adata.var)
 
     # Step 3
     with tiledbsoma.open(uri, "r") as exp:
@@ -1058,7 +1104,10 @@ def test_index_names_io(tmp_path, obs_index_name, var_index_name):
 
     soma_uri = tmp_path.as_posix()
 
+    original = adata.copy()
     tiledbsoma.io.from_anndata(soma_uri, adata, measurement_name)
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(soma_uri) as exp:
         bdata = tiledbsoma.io.to_anndata(exp, measurement_name)
diff --git a/apis/python/tests/test_platform_config.py b/apis/python/tests/test_platform_config.py
index 3849e33b53..680936c1e0 100644
--- a/apis/python/tests/test_platform_config.py
+++ b/apis/python/tests/test_platform_config.py
@@ -8,6 +8,7 @@
 import tiledbsoma
 import tiledbsoma.io
 import tiledbsoma.options._tiledb_create_options as tco
+from tiledbsoma._util import anndata_dataframe_unmodified
 
 HERE = Path(__file__).parent
 
@@ -27,6 +28,7 @@ def adata(h5ad_file):
 
 def test_platform_config(adata):
     # Set up anndata input path and tiledb-group output path
+    original = adata.copy()
     with tempfile.TemporaryDirectory() as output_path:
         # Ingest
         tiledbsoma.io.from_anndata(
@@ -53,6 +55,8 @@ def test_platform_config(adata):
                 }
             },
         )
+        assert anndata_dataframe_unmodified(original.obs, adata.obs)
+        assert anndata_dataframe_unmodified(original.var, adata.var)
 
         with tiledbsoma.Experiment.open(output_path) as exp:
             x_data = exp.ms["RNA"].X["data"]
diff --git a/apis/python/tests/test_registration_mappings.py b/apis/python/tests/test_registration_mappings.py
index bcfa2e838d..15e3d15d06 100644
--- a/apis/python/tests/test_registration_mappings.py
+++ b/apis/python/tests/test_registration_mappings.py
@@ -12,6 +12,7 @@
 
 import tiledbsoma.io
 import tiledbsoma.io._registration as registration
+from tiledbsoma._util import anndata_dataframe_unmodified
 
 
 def _create_anndata(
@@ -720,6 +721,8 @@ def test_append_items_with_experiment(soma1, h5ad2):
 
     adata2 = ad.read_h5ad(h5ad2)
 
+    original = adata2.copy()
+
     with tiledbsoma.Experiment.open(soma1, "w") as exp1:
         tiledbsoma.io.append_obs(
             exp1,
@@ -744,6 +747,9 @@ def test_append_items_with_experiment(soma1, h5ad2):
             registration_mapping=rd,
         )
 
+    assert anndata_dataframe_unmodified(original.obs, adata2.obs)
+    assert anndata_dataframe_unmodified(original.var, adata2.var)
+
     expect_obs_soma_joinids = list(range(6))
     expect_var_soma_joinids = list(range(5))
 
@@ -827,6 +833,8 @@ def test_append_with_disjoint_measurements(
 
     anndata2 = anndata1 if use_same_cells else anndata4
 
+    original = anndata2.copy()
+
     rd = tiledbsoma.io.register_anndatas(
         soma_uri,
         [anndata2],
@@ -842,6 +850,9 @@ def test_append_with_disjoint_measurements(
         registration_mapping=rd,
     )
 
+    assert anndata_dataframe_unmodified(original.obs, anndata2.obs)
+    assert anndata_dataframe_unmodified(original.var, anndata2.var)
+
     # exp/obs, use_same_cells=True:                       exp/obs, use_same_cells=False:
     #    soma_joinid obs_id cell_type  is_primary_data       soma_joinid obs_id cell_type  is_primary_data
     # 0            0   AAAT    B cell                1    0            0   AAAT    B cell                1
diff --git a/apis/python/tests/test_registration_signatures.py b/apis/python/tests/test_registration_signatures.py
index fd51a3944d..777d91e26e 100644
--- a/apis/python/tests/test_registration_signatures.py
+++ b/apis/python/tests/test_registration_signatures.py
@@ -6,6 +6,7 @@
 
 import tiledbsoma.io
 import tiledbsoma.io._registration.signatures as signatures
+from tiledbsoma._util import anndata_dataframe_unmodified
 
 HERE = Path(__file__).parent
 
@@ -28,7 +29,11 @@ def test_signature_serdes(canned_h5ad_file, canned_anndata):
     assert "var_schema" in text1
     assert sig == signatures.Signature.from_json(text1)
 
+    original = canned_anndata.copy()
     sig = signatures.Signature.from_anndata(canned_anndata)
+    assert anndata_dataframe_unmodified(original.obs, canned_anndata.obs)
+    assert anndata_dataframe_unmodified(original.var, canned_anndata.var)
+
     text2 = sig.to_json()
     assert sig == signatures.Signature.from_json(text2)
 
@@ -36,7 +41,11 @@ def test_signature_serdes(canned_h5ad_file, canned_anndata):
 
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+
     uri = tiledbsoma.io.from_anndata(output_path, canned_anndata, "RNA")
+    assert anndata_dataframe_unmodified(original.obs, canned_anndata.obs)
+    assert anndata_dataframe_unmodified(original.var, canned_anndata.var)
+
     sig = signatures.Signature.from_soma_experiment(uri)
     text3 = sig.to_json()
     assert sig == signatures.Signature.from_json(text3)
@@ -48,11 +57,16 @@ def test_compatible(canned_anndata):
     # Check that zero inputs result in zero incompatibility
     signatures.Signature.check_compatible({})
 
+    original = canned_anndata.copy()
     sig1 = signatures.Signature.from_anndata(canned_anndata)
+    assert anndata_dataframe_unmodified(original.obs, canned_anndata.obs)
+    assert anndata_dataframe_unmodified(original.var, canned_anndata.var)
 
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
     uri = tiledbsoma.io.from_anndata(output_path, canned_anndata, "RNA")
+    assert anndata_dataframe_unmodified(original.obs, canned_anndata.obs)
+    assert anndata_dataframe_unmodified(original.var, canned_anndata.var)
     sig2 = signatures.Signature.from_soma_experiment(uri)
 
     # Check that single inputs result in zero incompatibility
@@ -73,6 +87,11 @@ def test_compatible(canned_anndata):
     # Check incompatibility of modified AnnData
     adata3 = canned_anndata
     del adata3.obs["groups"]
+
+    original = adata3.copy()
     sig3 = signatures.Signature.from_anndata(adata3)
+    assert anndata_dataframe_unmodified(original.obs, adata3.obs)
+    assert anndata_dataframe_unmodified(original.var, adata3.var)
+
     with pytest.raises(ValueError):
         signatures.Signature.check_compatible({"orig": sig1, "anndata3": sig3})
diff --git a/apis/python/tests/test_update_dataframes.py b/apis/python/tests/test_update_dataframes.py
index 484f19ab31..0325a15167 100644
--- a/apis/python/tests/test_update_dataframes.py
+++ b/apis/python/tests/test_update_dataframes.py
@@ -9,6 +9,7 @@
 
 import tiledbsoma
 import tiledbsoma.io
+from tiledbsoma._util import anndata_dataframe_unmodified
 
 HERE = Path(__file__).parent
 
@@ -30,7 +31,10 @@ def adata(h5ad_file):
 def test_no_change(adata, readback):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o1 = exp.obs.schema
@@ -46,6 +50,8 @@ def test_no_change(adata, readback):
     with tiledbsoma.Experiment.open(output_path, "w") as exp:
         tiledbsoma.io.update_obs(exp, new_obs)
         tiledbsoma.io.update_var(exp, new_var, "RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o2 = exp.obs.schema
@@ -59,7 +65,10 @@ def test_no_change(adata, readback):
 def test_add(adata, readback):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         exp.ms["RNA"].var.schema
@@ -82,9 +91,13 @@ def test_add(adata, readback):
 
     new_var["vst.mean.sq"] = new_var["vst.mean"] ** 2
 
+    new_obs_save = new_obs.copy()
+    new_var_save = new_var.copy()
     with tiledbsoma.Experiment.open(output_path, "w") as exp:
         tiledbsoma.io.update_obs(exp, new_obs)
         tiledbsoma.io.update_var(exp, new_var, "RNA")
+    assert anndata_dataframe_unmodified(new_obs, new_obs_save)
+    assert anndata_dataframe_unmodified(new_var, new_var_save)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o2 = exp.obs.schema
@@ -105,7 +118,10 @@ def test_add(adata, readback):
 def test_drop(adata, readback):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         exp.ms["RNA"].var.schema
@@ -120,9 +136,13 @@ def test_drop(adata, readback):
     del new_obs["groups"]
     del new_var["vst.mean"]
 
+    new_obs_save = new_obs.copy()
+    new_var_save = new_var.copy()
     with tiledbsoma.Experiment.open(output_path, "w") as exp:
         tiledbsoma.io.update_obs(exp, new_obs)
         tiledbsoma.io.update_var(exp, new_var, "RNA")
+    assert anndata_dataframe_unmodified(new_obs, new_obs_save)
+    assert anndata_dataframe_unmodified(new_var, new_var_save)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o2 = exp.obs.schema
@@ -138,7 +158,10 @@ def test_drop(adata, readback):
 def test_change(adata, readback):
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o1 = exp.obs.schema
@@ -154,11 +177,15 @@ def test_change(adata, readback):
     new_obs["groups"] = np.arange(new_obs.shape[0], dtype=np.int16)
     new_var["vst.mean"] = np.arange(new_var.shape[0], dtype=np.int32)
 
+    new_obs_save = new_obs.copy()
+    new_var_save = new_var.copy()
     with tiledbsoma.Experiment.open(output_path, "w") as exp:
         with pytest.raises(ValueError):
             tiledbsoma.io.update_obs(exp, new_obs)
         with pytest.raises(ValueError):
             tiledbsoma.io.update_var(exp, new_var, "RNA")
+    assert anndata_dataframe_unmodified(new_obs, new_obs_save)
+    assert anndata_dataframe_unmodified(new_var, new_var_save)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o2 = exp.obs.schema
@@ -174,7 +201,10 @@ def test_change_counts(adata, readback, shift_and_exc):
     shift, exc = shift_and_exc
     tempdir = tempfile.TemporaryDirectory()
     output_path = tempdir.name
+    original = adata.copy()
     tiledbsoma.io.from_anndata(output_path, adata, measurement_name="RNA")
+    assert anndata_dataframe_unmodified(original.obs, adata.obs)
+    assert anndata_dataframe_unmodified(original.var, adata.var)
 
     with tiledbsoma.Experiment.open(output_path) as exp:
         o1 = exp.obs.schema
@@ -207,16 +237,25 @@ def test_change_counts(adata, readback, shift_and_exc):
     )
 
     if exc is None:
+        new_obs_save = new_obs.copy()
+        new_var_save = new_var.copy()
         with tiledbsoma.Experiment.open(output_path, "w") as exp:
             tiledbsoma.io.update_obs(exp, new_obs)
             tiledbsoma.io.update_var(exp, new_var, measurement_name="RNA")
 
+        assert anndata_dataframe_unmodified(new_obs, new_obs_save)
+        assert anndata_dataframe_unmodified(new_var, new_var_save)
+
     else:
         with tiledbsoma.Experiment.open(output_path, "w") as exp:
             with pytest.raises(exc):
                 tiledbsoma.io.update_obs(exp, new_obs)
             with pytest.raises(exc):
                 tiledbsoma.io.update_var(exp, new_var, measurement_name="RNA")
+
+        assert anndata_dataframe_unmodified(original.obs, adata.obs)
+        assert anndata_dataframe_unmodified(original.var, adata.var)
+
         with tiledbsoma.Experiment.open(output_path) as exp:
             o2 = exp.obs.schema
             v2 = exp.ms["RNA"].var.schema