So I've come across this problem a couple of times in the past. I don't think I ever actually managed to fix it, I think it may have just have gone away. It was however on a different version of Max. Basically, I'm in the process of optimizing my mesh and after collapsing two or more verts together and deciding against it,…
may be related to old max version. but yes this happens, undo is not perfect. especialy with applying certain modifiers, there is no way back. so save often :D some stuff undo does is not fixed as easily as broken normals.
I sometimes have this when I bring meshes over to max from maya. These meshes stay bugged - i.e. you can fix the undo issues but it may just keep happening again and again. I usually just export from max as obj and import the mesh again - in most cases the mesh remains undo bug free from then on.
Undo as such is bugged. you learn to work around it through the following steps: - perform more or less exotic action in max (ranging from welding verts with 'preserve uvs' to changing settings in your path deform modifier) - don't like the results; undo - mesh explodes - weep; reload autosave from 5 minutes ago (that's…