Let me preface this by saying that I’ve been playing about with Hammer on bm_c2a2a - as a result, it doesn’t link to c2a2b at the moment, so I have to use the map command directly to load anything else in OaR. I don’t know if that would affect the issue or not, but I haven’t modified c2a2b or c2a2c yet. Anyways.
In the missile launch area, on the right side when entering through the fence, there are two vents next to each other.
The vent grills have some… interesting collision detection.
By just pushing against them and jumping, it’s possible to get stuck inside the vent’s hitbox:
And jumping on top of the grill will treat the player as if they’re falling - once they move far enough away from the grill, they’ll plummet to the ground and take fall damage depending on how long they were floating.
I haven’t been able to recreate it so far, but I also managed to turn myself into a rocket by getting stuck on the vent and using explosives to kill myself:
Video of the fall damage bug here.