Weird graphical glitch

ok, sometimes, when i play, at once the scenery just changes.

Instead of the normal textures, there are all sorts of images on the floors and walls. Often there are also some images off ranks, guns or items.

The 3d environment is left intact, so it has to be something with the overlays.

when i press alt tab to go to another window ( firefox or whatever is open) and switch back to crossfire, all is ok again

here is an example