You mentioned Summer, and you are in New Jersey. Is is possible that you painted on a humid day, and some moisture got trapped under or in the primer, messing up its adhesion to the model's body?
It's interesting you mention that Peter because while I do make every attempt to be aware of the ambient conditions it's possible this was done under less than ideal conditions. But this same situation occurred with another model I painted with Dupli-color after the summer.