Indoors and Outdoors
It seems that if a room is too large it is considered outdoors, a room that is 13x8 with all walls floors and ceilings will be considered outdoor, but if you just build a wall through the center of the room it is considered indoors.
Version:
0.23.0.40
Fixed In:
A room (and thus indoor detection) is limited to 100 tiles atm, we're going to expand this.