My wife and I both have Orlieb handlebar bags, and have not had any problems with either of them for the 5 years we have used them. They have seen a lot of use and the snaps get used a lot. I carry my camera in mine and on a trip last summer took about 4500 photos. On three trips this year I took about the same number of pictures. That is a lot of unsnapping and snapping. I make it a habit to snap my bag when I remove the camera which increases the number of times the snaps get opened and closed. With the amount of use my bag has received, the snaps are really easy to open and close.
I was actually unpacking my panniers and bar bag as I browsed the forum. We just got back from a month-long tour today. After reading some of the posts I tried my snaps. What I found when I actually thought about it is that I don't use those little tabs to open the snaps. I slide my hand between the lid and the bag with fingers on each side of the snap to pop open the snaps. I suspect this results in a motions much like djb described in his post above.
Originally posted by djb
I strongly suspect that given that this has happened to two of them, it is how you are pulling at it. I find that if I pull upwards, its hard as hell to open, but if I pull perpendicularly forwards, towards me, it unpops easily.
I noticed this early on when it was frustrating to open at times, until I twigged to the "pulling it towards me" with no upward angle involved.