This problem can be seen in both the animation editor and in the 3d importer widget and maybe even other places in studio where bones are rendered. When importing a MeshPart that is rigged with bones, the visualization of the bones in the 3d importer widget and the visualization of the bones in the animation editor (after the import is complete) display the bones incorrectly.
When importing a skinned MeshPart, the wrong bones are highlighted when you click on them. In the image below I have selected the ‘toe’ bone of my custom character in Blender.
When I click on this toe bone in the 3d importer widget, it highlights the wrong bone.
In fact, it doesn’t even show the ‘toe’ bone at all!
Similar to the 3d importer, the ‘leaf’ bones of the bone hierarchy only render the first node of the bone. The rest of the bone is not shown. This leads to problems such as below where in your modelling software such as Blender you can see your bones exist, but when you go to animate your mesh it’s as if the bones are gone.
Diving into the problem even further, it seems that maybe the leaf bones are being drawn backwards. In this image you can see that the under arm’s bone is slightly darker than the upper arm bone to the left. I am thinking that maybe the leaf bones are being drawn on top of their parent bone instead.
Note that these leaf bones do exist. The problem is that they simply aren’t being rendered correctly.
In both the animation editor and the 3d importer widget I expect all bones to be shown correctly between the bone’s starting point and end point. So no missing toes or fingers.