I've got one of these couplings and love it so thought I'd contact OzHitch for comment.
Well it seems OzHitch has just changed hands. The new owners are extremely helpful and commented thus "we believe the problem has occurred in the use of a weight distribution system when doing a U turn"
Fair enough, doubt the original design considered possibilities like that. Presumably the weight distribution thing has levered the fork from the end of the shaft.
Anyway, they are shipping me out a new shaft/fork so I can lose the paranoia on our next trip.
Excellent service from OzHitch. No BS and no ducking for cover or not answering emails.
I still wouldn't have anything else!
very satisfied owner.