User-contributed fix; bypassed the contact form so no #Hnnnn number.
On the Gnome King's Wine Cellar version of Mines' End, a couple of
wall stubs in the lower far right were diggable, unlike all other
walls on the level. One single-spot wall stub was leftmost of three
undiggable spots, wall+floor+stone. The floor spot wasn't noticeably
different from normal (not sure whether digging a pit was prohibited)
but the stone one was.
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