I've been in the business for 23 years and have had only a few poblems with vinyl that has gone bad. I know some shops don't like Avery vinyls but I have been using them for many years with no problems. When the decals fall off they still have all their adhesive qualities, like someone else said - the glass seems to create a moisture layer underneath the decals after they have been adhered.
My customer came back yesterday to have the repairs done from the original install on Friday of last week. I used a multitude of cleaners...Bon Ami, Re-Mov, Methol , checked all the other decals that had not fallen off (they seemed secure) and sent him on his way with my fingers crossed.