Oh, never mind. I just figured it out with a little bit of detective work. There are crease marks on the paper right on the boundary of the fogged part. It looks like the corner of the paper was pinched by the door as it was closing. This means that the light trap IS working, and everything is fine! I'm ready to use the dispenser!!!!
That's the problem with loading and unloading the paper in complete darkness - you have no idea what is going on.