I have never had problems with this though. All I use for primer and clear and reducer is all SPI. Base I get from a guy off SPI forums in NJ which is R-M and high quality stuff. I have always used PPG and then tried DuPont a few times and their chromabase was fine but didn't care for it too much and then tried out the R-M he sent and like the stuff. I stick to the same stuff usually because it's what I know and never have problems with. I switched from the nason on this fender, stripped the fender down and use PPG and still, same problem. The clear was not put on heavy at all. Medium coat then second coat a wet coat. First medium coat started to bubble RiGHT away. I even tried a light coat and same thing. I used older clear at first and thought that was the probelm so bought new clear, sanded it back down and started over. Same thing with the new clear. I let the fender bake in the sun for a whole day and then put it in the shop, kept at room temp with a little Holmes heater next to it.
I have painted cars, hoods, bumpers, golf carts and everything in my garage with no problems ever. Now this is happening no matter what I change.