I had this happen on my first topflite spitfire. I glassed it in the early spring with deft brushing lacquer. Painted over it with rattle can paint. When i took it out to fly and set it in the sun it got blisters on it. The weather was in the mid-50s to low 60s as the day went on. All i could figure out was the deft had not cured completely and it was a result of off gassing.
I now use water based water based polycrylic. Use the same procedure. See link below:
http://www.wyliewarbirds.com/howto/howto.htm