I have 2 identical surfaces, one at -z and other at +z location. They both
have a transparent Material on the front side and a non-transparent
BackMaterial on the other side.
<AmbientLight ... />
When I rotate this model group around the y-axis, the behavior appears to be
different depending on the order the GeometryModel3D shows up on the list.
The first one seems to be non-transparent. I can reverse the order and the
other surface become non-transparent. Is this the expected behavior or am I
doing something wrong?