Amazingly, there was no damage to the shredder, the hitch, the bike rack, the bike, or me. The shackle pivoted on its mounting, the eyebolt rotated freely, and the trailer just "fell right over", resting on the framework over the left wheel and (sigh) scraping up the paint, which I have to sand down and patch. Aside from the paint, there was no damage to the trailer, despite its taking a fall with 30+ pounds of load. Well, actually there are a couple of gouges inside the plastic bin (big deal).
This incident makes me believe very strongly that you should use the official Donkey hitch if you carry a child on the seat. The CoG for a 40-lb kid sitting in about the same attitude as the shredder would be almost identical, and it would have been just that easy to dump the kid. This would have cost more than paint. So be careful with that living cargo.