Somewhere....on a forum.....there was a thread on how to fix them if your material is nopt torn. Basically, a good quality spray adhesive, pull the material down to expose the back and the panel, tape off all items you want to keep the glue off of,,,,spray....follow directions on sticking parts together. Most have had good luck with this for some time after completion.
If I find the posts, I will return and post that info.
Here is one....but not the one I remember...
http://forums.themustangsource.com/f692/door-panel-problems-any-suggestions-477520/#post6065394
Here is the one I was referencing...
http://mustangforums.com/forum/2005...on/555655-door-panel-leather-sagging-fix.html