That just goes to prove that bolts should NEVER be implicitly trusted, but at the very least a couple twists by hand should have kept the hanger and nut in place.
As my friend was climbing the .11a at Mt. Gorgeous, this bolt came flying off the wall while he was being lowered. It was the 5th bolt, so he wouldn't have hit the ground if he fell on it, right? Well, he did skip the first 2 bolts for convenience, and unclipped the 4th after he clipped the 5th. So why is his belayer frowning and he's smiling?