Ok after not being able to let this go ( dog with a bone) i think i got it down. when stealing pollen, the door is up , this makes the bees go into the trap and up the side where the pollen is stripped. When not taking pollen the door is put down, the bees go through the little holes and straight ahead where the pollen is not stripped because the entry at this point is bigger.
HA at least I think that is it. :-D :-D