Button on a Movieclip question

Let’s say MovieClipA is 100px x 100px. When I rollover MovieClipA, it makes MovieClipB go to ._alpha = 10. When I rollOut MovieClipA, MovieClipB goes back to ._alpha = 100. This is working as I want it.

Now, when I put a button onto MovieClipA, when I rollover the button, it acts like MovieClipA has had a rollOut, and MovieClipB goes to ._alpha = 10.

How do I prevent this? How do I code it, so when I work the button, MovieClipA stays in the rollOver state? How do I keep MovieClipA from going to rollOut when I go over the button?

thanks so much,
A