I've also had the gloss paint from a matt tin problem. Always from a new tin, and as has been mentioned in earlier posts, upon using the same paint for the second time the finish was matt.
I learned by accident that if you open a new tin and leave it for a while before use this can seem to fix the problem.(By allowing air to get at it?) I'm not claiming this to be definitive
'cure', but it seemed to work for me. Having said that I have always found Humbrols whites to be a nightmare, and so avoid them!
As for Revells range of paints, I used these for my aircraft when I was in Germany as they were the most commonly stocked, but I find that they become too thick especially if the
weather is too hot or too cold. Although I managed to paint a King Tiger with them no problem in the middle of a Bosnian summer...
Again, this is just what I've found, so don't shoot the messenger! I guess it's just personal choice and what ever works best for the individual.