However I was using regular Vallejo Model Color thinned down with their thinner, and it cracked.
I let it dry, and went over it again with the same color but this time thinned with distilled water, and it didn't seem to have the same cracking effect.
Left me to believe that it wasn't actually the paint, but the something in the thinner that reacted with the hairspray. Vallejo air would have some of the thinner it in, which could be why it cracked. I don't recall the brand of hairspray I used.
Fortunately for me, I was doing it on a Japanese Zero...heavily chipped, and the cracking just sort of worked into the chipped paint.
It is possible that it has something to do with the drying of the paint too....as they dry pretty quickly, it might be worth an experiment by adding some Liquitex to the paint to slow the drying down, to see if it keeps it from cracking. Worth a shot anyway.