2005 Gas cap problem

My mom's got a 2005 Rendevous she bought new in June. So far she loves it. She drive the heck out of it too (it's got about 10000 miles on it already... my family puts a lot of miles on our vehicles). Anyway, here lately, the gas cap has been coming loose on it's own and showing up in the messege center. She tightens it, and it takes a while for the messege to go away, but it eventually does, only to come back later when the cap comes loose again. Anyone with a similar problem or a fix? Thanks!

I have to say, in all my years of working on cars, this is a first!

It's still under warranty, so have the dealer replace the gas cap, I'd guess that the mechanism to prevent overtightening is working before it tightens fully. a new cap should fix it if thats whats wrong.

Yea, I told her to take it to the dealership. I don't know if she will or not. Really, it's her problem... I just don't want to hear about it. If something is wrong with a vehicle I'm usually the one who has to fix it.