[CocoaSpud]

Each art slot needs to have the same template format for the wall/door/overlay. The slot's format is determined from the wall, then the door, then the overlay. That is, if no wall is loaded then the door determines the format. You can have a different format in every slot though. Lord Killjoy's suggestion is the best way to go about fixing things.

Each template defines more than the source pixel coords for the file, it includes destination pixels, offsets, and so on. The destination coords apply to the entire slot, and the walls/doors/overlays are drawn relative to them. Letting the doors be a different format would let the door source pixels be found ok, but they would be drawn in the wrong place on screen. Although it is not impossible to give walls and doors there own format support, it would require a major update of the viewport graphics code. Each wall/door/overlay would need it's own set of destination coords and offsets. I'm hesitant to undertake such a job at this point, but I can add it to the list of future tasks - those that get worked on when the major missing features are completed (like magic).