Preserve Underlying Transparency has leaking edges

Actually, drop shadow does cause such a problem. Try to duplicate the bubble, remove drop shadow, and use it as an alpha track matte for the text

Impossible to know. You need to provide screenshots of the actual appearance, timeline and effects as opposed to describing invisible elephants. Chances are you are simply not understanding compositing order and thus messing up things. A different workflow may be required, but without any understanding of your project structure we can't advise.

Mylenium