Thanks for playing! Yes, it was a bug because it's programmed that you can't move in a direction if there is a wall in that direction, but the movement of the red blocks happens after the main movement, so you can enter one wall block without that restriction. I discovered it while doing the "The lava is floor" level,  and thought that I could use it as a new mechanic instead of fixing it. In that level I also discovered that you could go out of bounds because there is only a wall of blocks enclosing each level, and the background, which is in the same color than the wall blocks, lets you move through it, which inspired the "Out of bounds" level.