diff --git a/packages/blocks/src/api/test/registration.js b/packages/blocks/src/api/test/registration.js
index f4df432976bc12..cc339e59d27053 100644
--- a/packages/blocks/src/api/test/registration.js
+++ b/packages/blocks/src/api/test/registration.js
@@ -1703,6 +1703,43 @@ describe( 'blocks', () => {
 				'Block bindings source "core/test-source" is already registered.'
 			);
 		} );
+
+		it( 'should correctly merge properties when bootstrap happens after registration', () => {
+			// Register source in the client.
+			const clientOnlyProperties = {
+				getValues: () => 'values',
+				setValues: () => 'new values',
+				getPlaceholder: () => 'placeholder',
+				canUserEditValue: () => true,
+			};
+			registerBlockBindingsSource( {
+				name: 'core/custom-source',
+				label: 'Client Label',
+				usesContext: [ 'postId', 'postType' ],
+				...clientOnlyProperties,
+			} );
+
+			// Bootstrap source from the server.
+			unlock(
+				dispatch( blocksStore )
+			).addBootstrappedBlockBindingsSource( {
+				name: 'core/custom-source',
+				label: 'Server Label',
+				usesContext: [ 'postId', 'serverContext' ],
+			} );
+
+			// Check that the bootstrap values prevail and the client properties are still there.
+			expect( getBlockBindingsSource( 'core/custom-source' ) ).toEqual( {
+				// Should use the server label.
+				label: 'Server Label',
+				// Should merge usesContext from server and client.
+				usesContext: [ 'postId', 'postType', 'serverContext' ],
+				// Should keep client properties.
+				...clientOnlyProperties,
+			} );
+
+			unregisterBlockBindingsSource( 'core/custom-source' );
+		} );
 	} );
 
 	describe( 'unregisterBlockBindingsSource', () => {
diff --git a/packages/blocks/src/store/reducer.js b/packages/blocks/src/store/reducer.js
index 5e0714b6064fde..2f141fb0cf9927 100644
--- a/packages/blocks/src/store/reducer.js
+++ b/packages/blocks/src/store/reducer.js
@@ -372,19 +372,17 @@ export function collections( state = {}, action ) {
 }
 
 export function blockBindingsSources( state = {}, action ) {
+	// Merge usesContext with existing values, potentially defined in the server registration.
+	const existingUsesContext = state[ action.name ]?.usesContext || [];
+	const newUsesContext = action.usesContext || [];
+	const mergedArrays = Array.from(
+		new Set( existingUsesContext.concat( newUsesContext ) )
+	);
+	const mergedUsesContext =
+		mergedArrays.length > 0 ? mergedArrays : undefined;
+
 	switch ( action.type ) {
 		case 'ADD_BLOCK_BINDINGS_SOURCE':
-			// Merge usesContext with existing values, potentially defined in the server registration.
-			let mergedUsesContext = [
-				...( state[ action.name ]?.usesContext || [] ),
-				...( action.usesContext || [] ),
-			];
-			// Remove duplicates.
-			mergedUsesContext =
-				mergedUsesContext.length > 0
-					? [ ...new Set( mergedUsesContext ) ]
-					: undefined;
-
 			return {
 				...state,
 				[ action.name ]: {
@@ -401,8 +399,13 @@ export function blockBindingsSources( state = {}, action ) {
 			return {
 				...state,
 				[ action.name ]: {
+					/*
+					 * Keep the exisitng properties in case the source has been registered
+					 * in the client before bootstrapping.
+					 */
+					...state[ action.name ],
 					label: action.label,
-					usesContext: action.usesContext,
+					usesContext: mergedUsesContext,
 				},
 			};
 		case 'REMOVE_BLOCK_BINDINGS_SOURCE':