Yes it's not necessarily a warranty issue. (hey where did itsatdm's post go?)
It could've been the rivnut that was flawed or it could've been the bolt. The bolts do get a rough check when they are put together with the top racks and in my experience it's more to do with the rivnut.
That being said maybe we'll start testing each and every bolt to be sure!
Some dealers are more willing than others so feel it out first.
1. Have they had it happen? (you're "setting the table" here)
2. If so how did they fix it? Do they have the tool? rivnuts?
3. Is it a warranty thing? If not how much will it cost me?
If it costs (too much) and they have the parts :
4. Can I buy the right size rivnut from you?
Then do it yourself.
As I said try to get the bolt out first. Anything you can do to make it fast and easy for the dealer (if you're getting them to do it) will mean less of a headache for them. It's really time they need (want) to charge for.
BTW if you can get the bolt out then try to tap it first, then use the tool to re tighten the rivnut. If that fails (or seems weak) then replace it.