ok, tested it again (with decals on/off). strangely enough the 'fog' appeared near the end of the game. we had some frags before that (suicide in the pit as well) and it didn't show up. only later, without any reason..
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dont have time now, but will test it tomorrow with different graphics driver versions.
the blood is cool, but its clouding the vision

The road of excess leads to the palace of wisdom.
- W.Blake