It may be just a glitch, but if it is, then it is non-harmful.
In Castle Creator mode, build walls on the second floor or above. Do not put floors next to the wall. When you test the file or play it, move up next to the set of walls. You will find that your character sticks to the walls, and will glide along as if there were a floor. You can remain stuck through inside corners, but you will fall off from outside corners. This might help you create puzzles where the player has to cross a large chasm.