For example, if you place an object near water then remove it later, trying to land on that spot will crash the game. I had a lot of annoying problems in one of my map where the player can manually place teleporters and remove them later. So I suspect this problem to create corrupted squares later, which corrupts DO loops and so on.
Wondering is there is a way to get ALL infos about one square so we can restore later, regardless how we modded the square in between.