What's happening here is that when the room starts up, it must figure out what kind of floor to put under all the breakable walls. There's no floor information from the level editor because floor and breakable walls are on the same layer. So it has to guess.
It starts by finding all the "
connected components"
of breakable walls (meaning all the groups of breakable walls that are connected to each other), and looking at what kinds of floor squares border them. In this case, there are two such groups (they don't connect diagonally). The northeast square is obviously right next to normal floor, so the game puts normal floor under it. However, the other one is surrounded by walls, which provides no information about what floor is best. So it assigns it the type of floor that is most common in the room overall. In this case, there are twelve mosaic squares and eleven normal squares in the room. (It doesn't consider the floor under breakable walls, since it's only guessing at that anyway.) So it guesses the floor should be mosaic under the southwest breakable wall.
If you remove the northeast breakable wall, now there are twelve of each type of floor in the room, and the game tends to break ties in favor of normal floor over mosaic. So it assigns normal floor to the remaining breakable wall.
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I was charged with conspiracy to commit jay-walking, and accessory to changing lanes without signaling after the fact
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++Adam H. Peterson
