Bugged automap

[tombdust]

Playing the latest Steam version, my map often looks like this:

http://i.imgur.com/XhTiWUz.jpg

As you can see, the explored areas have the same color as the background, instead of looking dark brown or whatever. The map is confusing to use and I actually haven't been able to find the stairs to level two in that maze due to the map bug.

I'm using Windows 7. Restarting the game doesn't help. I've played with two characters so far, and the bug has been present with both characters, not with every dungeon but a large portion of them.