You might be onto something there Dave. I've been with him on three occasions when it popped out (his shoulder, I mean, not his JT).
Once was in Font on a burly 7A+ roof - after we'd all done it, Jonny boy, who had stopped groaning by now, muttered something about having another quick look. Pulls on and cruises the problem without incident.
The other two times have been winter climbing and in both cases, and also after a bit of groaning and cursing (the language was shocking), he continued to the top of the route seemingly unscathed.
Come on Jonny boy, come clean, you've been having us all on, haven't ya!?
Either that or it's some sort of wierd Hobbit magic.