Question about 3D collections

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?

Ben Root