That sucks man.
I've only had 3 days on mine so far. So far worst I've had is my back foot toe strap backing out during a run. Luckily it was on a green run. Was hoping it was just my fault but is that what you mean by coming loose?
i have had that problem a few times. now i'm very careful to make sure that my heel is all the way back. i think that since the highback is very curved at the bottom it tricks me into thinking my heel is all the way back, when really it isn't.