Re: What caused this?
Thats a condition known as blushing. The evaporation of the solvent lowers the temp of the painted object until it pulls water/humidity from the air. Its common to fast evaporating solvents like in lacquer and fast drying rattle cans. Not so common in slower paints like the old enamals. A top coat will set it right, but be sure to wait until the previous coat have dried enough or you might get a wrinkle finish. Used to own a body shop in Orlando, am well familar with this problem.