Alright, so here's a weird one.
Basically, there's a point (really, a whole vertical plane) in my map that sends you into the void--whether you're "in" the map or not.
It's kind of hard to describe so I uploaded a video:
As you can see, if you move away from the blue bridge structure towards the blackness, you pass into the grey void without actually reaching the end of the box--and as I demonstrate later, this happens outside of the map bounds as well. Actually, you're technically taken to the *other* side of the map--as if you'd gone so far in one direction that you looped around to the other (like what happens when you fall through a hole in an unsealed map).
I *don't* think it's because I exceeded normal map size limits (that's what those colored lines are supposed to represent in TrenchBroom, right?). I've already ruled out holes, at least those that BSP can detect, having tracked them all down with pointfiles and removed them. Any ideas?