I'm already using c_trace with USE_BOX to take care of all the slope walking and stair climbing, but the bounding box still goes to the feet because otherwise there are problems with getting stuck on ledges, and I would need another bounding box to make sure bullets could hit the player's feet. Anyway, wouldn't changing the bounding box change how USE_BOX affects the c_trace? This might be the problem.

I attempted to change the bounding box right before the main c_trace, and then change it back, but that just screwed it all up.

EDIT: Although, it seems that you're right. The bounding box is simply getting stuck, but that seems weird. I'm only changing the top of the bounding box, not the bottom.