Brightness fluctuation on Badham map(s)?

PlaysByShady

Please see this video, from 0:45 to 1:10

https://www.youtube.com/watch?v=OizzXrfn_wA#t=45s

As you will notice, when the camera is rotated around, the screen gets visibly darker at certain orientations, whereas it shouldn't really.

This is on 3.6.2, PC