I stumbled across an assembly created by someone else where the order of items in the feature tree is unusual:
Somehow, a bunch of components ended up between two component patterns, after the Mates. Furthermore, notice that LocalLPattern7 is a pattern of the component below it (409107). I can roll back the feature tree to before LocalLPattern8, but I cannot roll it back anywhere between the misplaced components. It will roll back to before LocalLPattern7, but misplaced components are still fully accessible and aren't greyed out.
If I drag all the misplaced components to where they would normally be (before the Mates folder), I cannot return then to their original incorrect positions.
I'm curious if anyone else has had this problem and knows if it is a file corruption issue or something else.