Huntschool, you are on the right track. I have not seen all the steps on moving parcels, just the unloading of BMCs from the truck at the local post office. As a carrier, I have not seen the opportunity for such a mishap at the local level. I would have to really think hard and work even harder to do it with the equipment that I use daily. An engine of some sort would be a plus.
This looks like a large conveyance full of parcels was being moved, and this parcel slipped partway out somehow and got caught by a doorway or supporting structure. The particulars of handling large amounts of parcels between General Mail Facilities, as I said, I have not seen. My post office was closed and its operations were moved to a GMF, so I hope to learn more firsthand through observation once we settle in and get routines to be a little more.. uh, routine.
Killdeer