How come simple doors can't be placed on the borders of rooms?

Pip Halsey

Level 4

I must be really missing something, because I can't put working simple doors on the borders of rooms. I can put double doors, prison doors, secret doors, and stairs doors, but simple doors won't work on the borders of rooms. I'd like my dungeon to not use double doors for every single room it has.

Silverquick

Level 14

That would be because Simple doors are used when you are sectioning off a room and using wall dividers to create multiple room structures within a space. ONLY Double Doors can be used between actual Tiles themselves.