At these coordinates (IWAD=TNT,MAP=MAP01,X=24,Y=252,Z=25) you climb up the stairs and punch the imp using the beserk fist. The imp is instantly gibbed, but he seems to explode around you, instead of in front of you; I was running forward at the time and so into the mess) and then you are stuck in the place you were when the imp is gibbed and you cannot move. The bobbing occurs when trying to move, but you can't actually move. It is as if your feet have become bogged down in the imp's remains. This is with the model pack.