Didn't find any help on Snarkpit so I thought I would give you guys a crack at this one
Having some issues with a lighting bug. I have tried lowering the -chop, removing nearby light entities or adding them, changing the number of bounces, adding ambient light, making the arch brushes entities vs world brushes, and remaking or rotating 180 degrees etc. the arches. No luck.
It seems to only happen with arches that are in a room where light from the sky brush can reach them, though...? That's the bug- you can see a 'ghost' of the arch around the doorway. It is the doorway over to the left that is in the pic, but several others in the map have similar issues.
Here is the map's profile (pics and download of the last beta) on Snarkpit if you want a closer look:
http://www.snarkpit.net/maps.php?map=2775
Any help would be appreciated. Think I'm going to focus on finished everything else on the map since this has me pulling my freaking hair out!