I had this problem, but I found that clear coating it, stops it, as it adds a harder layer over the top of the paint. Try only doing one or two very thin rubs with coarse, not putting too much on, something about the size of a 5 p coin, I think its about the size of an American 10 cents or 5 cents I think it was ten cents thats smaller, whichever one is the smallest, coin for one side for each coat, and then do about the same for the others, about two coats for fine and about two or three for finish, stop when it gets quite shiny. Then, to give it a proper shine, compunds just seem to smooth it, use Tamiya Modelling Wax.