Yeah, we have seen this before. I believe the basic problem is that there is sufficient looseness for the bags to come off the bike under exactly the right circumstances of forces generated by that very specific bump. One bag on my bike is pretty loose but the other one is reasonably tight.
There are a few solutions for this- the already mentioned 'pinning the bags'. Another is the steel rods that someone sells on Ebay. A third option is a tie- wrap wrapped around the handle on the saddlebag and onto the lifting rail above it on the bike. Of course that must be cut every time the bag is removed and a new one fitted.
I am going to just shim the latch on my bags so when they latch, there is a little pressure on the latch and no real 'jiggle room'. No evidence that that will prevent the problem but I think it will, it adds nothing that must be dealt with to put the saddlebags on / take them off, and basically will make the latches behave as they always should have IMO.
Brian
my 09, 74k miles, the bags are feeling loose, but never lost one. usually have some stuff in them.
not sure if there is a way to tighten the fitment up some.