Drop tanks won't drop

I have a Mustang that comes up with drop tanks. In the VC it has controls to drop these tanks. It says they are dropped...but they are still on the airplane. There is another Mustang file I have tried that appears to use a very similar model, if not the same exact one, and the tanks work fine on that one. So, how can I make these tanks actualy drop? Or not even be on the a/c at all?