Button inside a movie clip

1

So basically:

  1. I have a box shaped movie clip on _root which is kind of off-stage, so only the upper half is showing.
  2. When the mouse is on rollOver that upper portion, the whole clip moves upward so it shows the whole thing.
  3. I also have a button inside this movie clip. It’s part of that hidden portion.
  4. When I do rollOver everything works,except when I put my mouse over the button then the clip goes down again.

Why?