If your mask is pulling up the paint you just applied when you remove it, you're probably putting your paint down too thick resulting in a solid layer of paint bridging from the model onto the mask.
If your mask is pulling up paint from a previous color, the previous paint was probably put on too dry. See next suggestion.
If you use lacquers and you mist your paint on try spraying a wet coat of leveling thinner over it so it bonds to the lacquer under it.