MaterialStrain.plot() shows wrong preview

[adtzlr]

The preview of MaterialStrain with state variables is wrong

import felupe as fem

umat = fem.MaterialStrain(
    material=fem.linear_elastic_plastic_isotropic_hardening,
    λ=2.0,
    μ=1.0,
    σy=1.0,
    K=0,
    dim=3,
    statevars=(1, (3, 3)),
    tangent=False,
)
move = fem.math.linsteps([1, 1.8, 1.4], num=21)
ax = umat.plot(ux=move, bx=None, ps=None)
ax.lines[0].set_marker("o")

but this is correct:

mesh = fem.Cube(n=2)
region = fem.RegionHexahedron(mesh)
field = fem.FieldContainer([fem.Field(region, dim=3)])
boundaries, loadcase = fem.dof.uniaxial(field, clamped=False)
solid = fem.SolidBody(umat, field)
step = fem.Step(
    items=[solid], ramp={boundaries["move"]: move - 1}, boundaries=boundaries
)

job = fem.CharacteristicCurve(steps=[step], boundary=boundaries["move"])
job.evaluate()
fig, ax = job.plot(
    xlabel="Displacement $u$ in mm $\longrightarrow$",
    ylabel="Normal Force $F$ in N $\longrightarrow$",
)