Well, with glide mode on, you can snag a corner and still slowly work your way around right? Well that's whats happening with a ceiling plane thats above the entities origin. It's gliding down the z access trying to make its way into the vent. I move forward and push into a wall that has a vent without crouching, and wiggle my pan around and then I'm stuck in the wall. I turn around and move forward and I come out of the wall. I'm not modifying the player.z at all, simply moving it around with c_move. If players not crouching the c_move moves it to 32 units about the ground, if crouching makes its way to 16 units.