I used Humbrol acrylic for the first time a couple of weeks ago on my lifeboats, and the finish was c***........I'll never use that again.
I have also noticed that with the enamel paint which I use almost all the time, the satin and matt finishes also give a gloss until the paint has been used and opened to the air for some time.
To stir my paint I use a small electric 12volt drill on 6 volts, with a wire "curlyjig" attached and stir with that for a good 5 minutes, and then l leave the lid off for a couple of hours (if it's a new tin) before finally wisking it up again and using..............it seams to work and gets rid of the gloss effect.
Neil.