Hey deb, you might want to take a look at this.
It's not the only place where this happens: at the end of the dungeon, after the chase in the "maze", and I recall another place but I don't remember where.
Yeah it's usually north walls that do this. In the pictures you showed, the problem was that the banners I put on the wall were set so that the player could walk over them, which overrides the setting that says "no, you can't walk on these walls." It also happens if I don't put walls under the roof tiles, as by default you can walk onto ceiling tiles from below, for some reason.