I am trying to track down a problem in the 3D code, and I have noticed an
issue with Axes3D.add_collection3d(). It checks to see which collection
type you are passing in and will convert them to their 3D equivalent if
possible, and then calls .set_sort_zpos() afterwards. However,
.set_sort_zpos() was only defined for Poly3DCollections. Was there supposed
to be some sort of inheritance that was supposed to occur or something?