I think you have all explained the result I'm seeing when I attempted to paind a piece of the engine sub assembly. Instead of airbrushing, I tried to brush the black semi-gloss Tamiya paint onto the piece. The result was very bad adhesion of the paint to the surface being painted. Rather than adding more paint, I stopped and will wait for my spray boot to arrive later this month. Glad it was only one small piece. I can clean it up with Pine-Sol or Scale Master paint remover with out harming the plastic. Live and learn. Thanks for the tips all.