I remember reading somewhere on here that there was one guy riding down the road and a bag popped off....don't remember if he said why...
That was me last summer. I lost my left side bag on my '09 SERG O/B and was lucky enough to have someone find it and hunt me down while I was looking for it along the road.
I always take the bags off when I detail the bike. I've done this many times and have used the 1/4 turn fasteners on my Willy coupe without any issues. I know that when I put the bags back on Friday night after cleaning the bike that I had them turned to the lock position. I often lock, unlock and lock again to make sure that I have them in the wires and that I have them into the detent in the pins.
The road was fresh blacktop, but where there were creeks running under the road they would stop the blacktop for about a couple hundred yards and then start back up again. Sometimes the stop/start areas were not all that well marked. I was always able to slow down on the restart of the blacktop, but the stopping was not so easy at 60 mph and no warning where they stopped the fresh blacktop. On one of those spots the left bag fell off and skidded on the outside and did not roll or tumble, which is what saved the contents from flying all over. Both of the pins were still inside the bag and really looked good, no bends etc.
My insurance bought me a new fully painted SERG O/B left bag, but still with $500 deductible, it was not a good ride that day. At $1,700 for the prepainted bag, it's worth looking for an alternative to the 1/4 turn pins.
I've thought about Torx or some other anti-tamper bolts, which there are many available for not much money, but I now check my pins everytime I ride and I often reach back and feel for the bags just to make sure they are there.
The 1/4 turn pins are probably not the best way to attach our bags, but that's what HD does so we assume it's good enough.
Sorry for rambling, but I still have a VERY bad taste in my mouth for the pins and how they "just" came loose, albeit with a lot bumping going on.
I recommend that we all check these pins on every ride and even during the rides when we stop.