Button Work When Covered?

Hey,

Sorry if this question is rather newbish. I’m using Flash CS3. I have a button on a layer, and a movie clip on a layer on top of the button. The movie clip is partly transparent, so you can see the button on the lower layer. However, the button does not sense mouse-overs or mouse clicks when the other movie clip is covering it. I want the button to be able to work even when the movie clip is on top of it.

It worked correctly in Flash 8, but seems to have changed in Flash CS3. How do I do this in CS3?