Yep, it's definitely the clip 'riding-up' out of its slot.
The only cause I can think is that the axle is flexing under the load of the A.I. causing stress
on the clips, pushing them up. Here are a few more pics of the issue/damage caused:
The temporary solution I've found is to attach a small cable-tie to the 'open end' of the clip
(while the twist cap is in place and the wheel is on the cart). No need to pull the cable-tie
tight, just enough to prevent the clip from opening. The twist mechanism still works and
it appears to prevent the problem.
I'm not sure how good a solution it is, as I've no idea how much force is being transferred
to the clip. I guess time will tell.
In the meantime I'll contact my local Hobie dealer (on the recommendation of the local Wheeleez
dealer) to see about a warranty claim on the damage.