This happened to me at the B pillar, passenger side. The strap just completely fell off the bar, rivets slipped right through the strap.
I guess they aren't entirely necessary, but if you put the top down and up a lot the straps can get all twisted and get caught on stuff. If you want to avoid the headache with the dealer, and fix it for good you can try what I did:
- Take a dremel w/ cut off wheel and cut the head of the rivet off and let the shaft slip out of the bar.
- Drill out the hole that the rivet was through and find a small bolt and push it up through the bar & the strap.
- get a 1/2" or so sized washer to place on the bolt between the strap and bar.
- Secure with nut
I did this probably almost a year ago, and its held up ever since AND since the top of the bar is always covered (even when the top is folded down) you can't tell it's not those factory "rivets" holding it on.