Black and White masking principles (help please)

In typical programs like Photoshop, masks are determined by black or white and even grey. I am however having a few problems in Flash.

I have a motion effect that reveals some text. Now When the motion effect comes back I want it to hide the text, but even when applying black to a seperate mask it does not works it reveals the text. I must be doing something wrong somewhere and really need to figure this out.

Can anyone help me out here?