(see screenshots below)
Ok above, You can see the outer walls for the shawdow and ice walls are orange and you can also see the walls take away the tiles too.
Above: You can see when the outer walls are deleted they leave a dirt patch tile.
Above: after I had commited the stairs disapeared and the walls got messed up with the tiles....
Maybe it's just those two that is known for this I'm not sure but I thought I'd post it incase.
