rdgrimes is the expert in these matters. 
I use the method he explained to me some time ago and I have no problem: find a perfectly flat surface, put a piece of A4 paper on it, put the disc on the paper, spray lightly and evenly, respect the spraying distance, and don't overdo it. If you want a better finish, it's better to wait for the fixative to dry, and put several light layers rather than a single heavy one.
The fixative will cause the problems you mention if you spray too close to the disc, if you're heavyhanded (too much spray), or if the surface is not perfectly flat.
Good luck 