This started happening today. I have not changed any settings for a couple of days and everything has been working fine. However, when the rail gun is fired and a rail marking is placed on a wall, a black octagonal shape appears for a second. I've adjusted video settings, deleted all my q3config files, even removed quake3 completely and reinstalled.
One thing I have noticed is the shape will only appear while playing Threewave over the internet. If I start a multiplayer game on my computer, the shape does not appear. It also will not appear in any other Q3 mod, even plain old Q3 deathmatch is just fine. The glitch is only on Threewave multiplayer. Any ideas?