Lighting/Glare Bug on HD Graphics?

[Gnuoy]

Players on my map report a bug, it seems to happen at the same in-game time. They say it like the brightness or contrast is randomly turned up, then it eventually goes away but comes back again. I've never encountered the bug but I only play on SD, and so many players have mentioned it that it must be a real bug.

Does anyone know what bug they are talking about or how to fix it? I just recommend they use SD graphics.