Seems I've stumbled across something odd, and I'm not quite sure how to fix it. I'm working on an Onslaught map, and the housing for my core has this.. platform above it, for players to spawn on, etc.
Anyways, here's a screen showing my issue exactly:
This only affects the brush, and the whole building thingy there is one big intersect additive brush. Does anyone have a clue what could be causing this?