How to reproduce the bug:
- have mirror mode OFF
- place a single part (i tried with wings) near the middle of the bay that would go red if placed using mirror mode.
- place another part/cube randomly
- activate mirror mode
- delete that part (the wing) using mirror mode ON
- press UNDO and the wing will never be reconstructed, the undo skips the wing and works properly for the rest of the build "history"