I had my 2003 explorer sitting in the sun for a half-hour and the heat seemed to make part of the tailgate warp and bow out. I can see that some kind of adhesive underneath gave way.

How have others of you dealt with this problem--I'm assuming mine isn't the only one that's done this.

 

I'd hazard a guess that the hatch has been 'repaired' at some point... and the adhesive used has outgassed and expanded under heat. Most likely the wrong adhesive? 'What's the stealership say?