Interesting thread! Last July I toured the country with my sister - I always keep 2 sets, one stays in the truck, the other in my pocket or in the trailer on the hook. One day *poof* one set disappeared...we scoured the place and found nada. We decided to wait to replace them to give time for the gremlin to cough them up. We then stopped at a mom and pop locksmith and had our entire set duplicated.
A couple days later my sister found the keys in one of her purse pockets that she never uses...must have dropped in that pocket rather than the one she uses...now I have two spares!