There is one edge case that can result in doors being moved to invalid surfaces within the editor: if a style has floor/ceiling corridors for singleplayer but not co-op, the singleplayer door is moved onto the floor/ceiling, then the mode is switched to co-op, you now have a co-op door on the floor/ceiling despite not having any valid corridors for that surface.

• Compiling will produce an error display with the message No corridors available for the <x> group! This should be changed to a more user-friendly message which uses nicer names for the groups (e.g. "singleplayer entrance door on a wall" instead of "Horizontal_Sp_Entry") and extra text explaining how it got into that state and how to fix it. (Could also enable the chamber display with the position of the door highlighted.)
• Moving the door back onto a wall can result in it being sideways, since DesiredFacing only gets added when there are valid floor/ceiling corridors. It should be present always, not really sure why it was made conditional to begin with.