Thats no real "glitch"
brightness 1 could be compared with tonemapping...
It just looks for the lightmaps brightness on your position and then it adjusts the tonemap for you... Its a more realistic feeling like going out of a dark cave and everything will blind you.
The "glitch" that you encountered is a problem with the visexport that the map has. It just thinks you cant see that spot and just doesnt render it. Its not paintballs fault. Thats related to bad mapping or bad export conditions.
Hope that explained well!