Carnage, can you just give it another light coat to cover the spots? If you're using Matt paint you have to be very careful of fingerprints or sweaty hands or water drops, etc even when the paint is fully dry. It seems to just leave a permanent stain on the paint surface. I've had this happen to me also and I had no choice that I knew of but to respray. BTW, are the Tamiya paints working better for you with the thinner?
Cheers...Snowy.