I can't find a pattern to it. All I know is that this happens on undo-ing terrains E.g. Cliff.
It also sometimes crashes when I undo a map with a black tile. Happened to me this morning, I didn't save my map so it got sent to the void and I can't send a crash report to the dev since I had no internet this morning.
I hope the dev sees this.
For newcomers, click here for discord links. Hopefully they aren't expired.
True. That bug exists a long time. It messed up the cliff terrains. I seldom use this button when the map has cliff type pictures. Normally I use eraser to clean cliff terrains.