For some reason, my colonists have started hauling from the 'output' stockpile, to the underground output that leads to it. There is a possibility that they're hauling to the pusher, but I can't really tell.
I've checked that there's no stockpile under the conveyors, but they're still doing it.
As amusing as it is to watch them try to make a perpetual ignorance machine, I would like to stop them wasting their time...