A bug a faced a couple of time recently with current version 2018.0.171: I had accidentally cleared a selection (like by clicking outside of the model) also while using SHIFT to use the path guessing feature, somehow the selection got cleared, tried to use Undo to restore it but it never went back. Kind of a problem when working for like 10 minutes on a selection and it all goes away.... I think it should be less easy to clear a selection. Today a simple accidental click outside the model and all is gone. I think there should should be a specific command to clear current selection so we don't do this accidentally.
Update: looks like the undo is also intermittently broken for moving island.