I am also experiencing this problem. I initially used some adhesive headliner spray, but that didn't work for long. Now the entire liner is sagging, so I'm going to take it in to have it looked at. I think that the edge came loose first and then the wind/summer heat caused the rest to sag as well. I'm also going to put wind blockers on my windows just to be safe.

P.S. If you don't already know, some chrysler dealerships don't know how to fix crossfires or don't have the parts on hand. I take mine to a friend that works at a Mercedes repair shop. It ends up being cheaper and A LOT faster.