Demonstrated in this recording at turn 5805 where my Staff of Firebolt gets deposited on a square occupied by a mirrored totem, making it impossible to retrieve except by using a potion of descent.
Later on turn 6737 I drink a potion of descent and I retrieved the Staff of Firebolt.
It seems like a bug rather than a feature because the auto-explore feature keeps on trying to move into the mirrored totem to retrieve the staff but it is impossible to retrieve via any means other than potions of descent.
Recording:
https://drive.google.com/file/d/1ONngHZjzX3FAVo7w0T-w98RRdxj0ZHYt/view?usp=sharing