I think it has to do with a problem in the entity's I/O system when there's a lot of lag on a server, (not Loafie's fault) similar to how sometimes the doors in Runway close randomly. I don't know if there's much we can do about it, as it's a pretty rare bug (I've only seen it 3 times since the Beta 3 release) and it gets reset at the end of the round.
Also, the ability to strafe into a very steep object/1 unit brush is a common source problem (some people consider it a feature). There are things that can be done about it, but it's not exactly worth pursuing right now.