When you set the shape of a part to “Ball” when all surfaces are set to “Smooth,” you get a low-poly version of a a sphere. This in itself could be a feature or a bug (I’m not sure which), but it’s useful since you can reduce the amount of polygons they have, lightening the rendering load. This is all fine and dandy, but the main problem with them is that the low-poly versions use the same collision model as the high-poly versions. The images below demonstrates the problems this can create:
An easy fix for this would be to implement some kind of alternate collision model for the low poly sphere. I don’t know how easy this would be with the current architecture, but it’s pretty irritating and it should be fixed.