Check out this interesting bug in Accursed Crown of the Giant King. As part of generating some levels, I create a structure with some stairs in the middle. Working on something else, I noticed that in some circumstances, the stairs would get a wall created right in front of them! See this screenshot:

Note that in this screenshot, the bug is the little half-wall in front of the stairs. In this case there is actually space for the player to get through the wall to the stairs, but with the bug, it is possible to completely block the stairs. There is also a full-wall in front of the stairs that is not a bug, but rather a secret door. Ignore that for now.

This bug happened because I created the structure just a little larger than usual, to match the rest of the level. Then, in this case, I failed to clear out enough of the wall in front of the stairs. The fix is easy enough; just extend the clear space by a couple of squares (depending on the size of the structure):

All fixed! Almost a one-liner, but took awhile to figure out just what the problem was.