If you try to draw on roomsurfaces without having a background pic, you get this nice CGA effect 8-)
Spoiler
(http://i.imgur.com/t77V8xT.png)
Unfortunately it also drops the framerate to 2-3 fps.
This also happens when you update the game to 32-bit and don't reload a dummy pic as room background.
It's not a major issue, but worth mentioning.