Ok I dropped it.
Right on the rails and tailgate. $6,000 mistake but how did it happen? I was solidly in the hitch, the tell tail flag was out of the way and I was able to put the locking pin in straight. I pulled against the trailer with wheel chocks in place and legs just up an inch - all okay. Raised legs and checked my trailer brakes and the pull popped the hitch jaw open. After getting the pin box out of the truck box I took off the hitch saddle plate. The locking pin for the jaw that goes through the hole in the handle had gone to the side of hole in the lower fixed locking tab apparently because the handle had not fully retracted. This allowed the handle to move and the jaw to open. Short of laying in the box to check it, it is nearly impossible to see if you have the pin in the lower hole. Not making excuses but this is a real bad design flaw. I am going to change the pin and from now on insert it upwards through the lower plate first. The handle will be marked with a with a contrasting colour so I can see that it is fully retracted. I post this as a caution to all who have or are contemplating buying this hitch in the hopes that it helps someone else avert such an accident. I have now read several accounts from others of exactly the same experience with this hitch. I shudder to think of this happening on the road. BTW the trailer had very minor cosmetic damage but I am going to check out the front framing around the pin box when I figure how to get at it. Any help in this regard would be much appreciated.