Although the heading is dated as 2007 Fatboy, it's not noted what sort of mileage the bike has, nor does the second incident - are these high mileage bikes?
Original post was of a bike with about 40k miles, I've had it from new and as far as I know the bolts have never been removed. The dealership take is to use the same bolt and washer as per parts catalogue. After the incident I've heard that Roadking have had the same issue.
As I've said I now check them as part of the critical fastener check.