It appears to be related to the widescreen bug. There's a fix for this posted in the links section.

Alternatively you could try fiddling with the game resolution config and the video driver settings. More details here:

http://graviteam.com/forum/index.php?topic=11121.msg31264#msg31264

The key here, I think, is to change the desktop resolution to something lower, before changing it back.
And don't restrict video modes in-game.

"It's fascinating to think that all around us there's an invisible world we can't even see.
I'm speaking, of course, of the World of the Invisible Scary Skeletons."