I've had this problem before, but I have never found a way to fix it. Basically, there's this phantom triangular player clip that extends out from a world brush plane that doesn't want to go away. There are no illegal or malformed brushes so I don't know what to make of it. Here's a crappy photoshop image to illustrate the problem.
Basically if you crouch, you can go under the triangle and it's like being in a small vent, but if you try to walk up to the ledge, you go up the ledge like there is a slope rising from the floor to the ledge which is not the desired behavior.
Admiral, why dont we just breach the hull after overriding the automatic hatchlocks closing procedure?My WebsiteNS Map Archive
Last time we did this an onos just put its fat **** inside the hole and lerks just farted a new athmosphere.
It looked so gross that we decided to never ever do this again.