Its not humidity affecting it is it? Or are you putting it on too thick?
I've had the problem with laquer drying hazy and not clear but not paint, i was never sure if i put it on too thick or if it was humidity. As i read a few articles pointing to the humidity causing haziness but i've only had the problem when doing quite thick coats (but not thick enough to run).
I've never had a problem with old paint from a rattle can, the warm water thing may help, i've never done it myself but have read if its quite cold it helps with adhesion