strayDog--
Wow. It's hard to envision how that could happen. I know I occasionally find one of mine has come off its roof-side hook and it's either standing up and just leaning back a bit or has flopped down. In either case, I can't envision that lock-down blade turning enough to fall off.
However, I just took a closer look at mine and I'm surprised to see how much they vary. Some extend through the 'nut' by five or six threads. But my right-front one doesn't extend through at all and is loose enough it might fall off given the right set of circumstances (you know, the ones I can't envision). Time for some blue loctite, I think.
Thanks for the heads-up.