This is one of the reasons I don't use Model Master paint. Metallics are particularly problematic. I am assuming that this is an enamel, but the comments apply to acrylics as well.
What is happening is that the silver pigment is floating to the surface, and teh paint film is not sufficiently strong to hold it there. This is either a formulation defect or the paint has gone bad. For the most recent problem, the solvents in the paint you are applying over the silver are attacking the surface of the silver paint. I assume you are airbrushing. If the paint has not gone bad, applying both the original silver and the overlying paint in multiple, thin coats may help.
I cannot recommend any enamel silver paint. I have recently used Humbrol with success, but they seem to have quality control problems, based on the number of complaints I've seen. Consider Alclad II—if you're doing organic solvent. They are lacquers, but excellent. For acrylics, the only metallics I can recommend are Hawkeye's Talon—superior paints, but read Hawkeye's instructions on his web site and watch the videos.