Whenever I launch Dxtory and launch Garry's Mod, it shows the FPS counter fine, I don't lose frames, and all's well. But as soon as I start recording, I will get a lighting glitch in Garry's Mod that makes everything seem brighter, which it is. I've recorded this a few times and can post it to youtube if needed. I have no clue if this is a known error, or if this is new but It's quite annoying and I cannot have recordings be buggy.
Indeed upload the video to YouTube since I don't quite get it what you referring to. Also what is your start recording key and does this glitch happen in other games?