I am using a movieclip as a mask to apply an effect on notes scattered around the screen in one of my games, but I don't understand what is happening with it...

Here, take a look:


The mask is made green on this shot to show the problem. The top note is acting normally, yet the bottom one, using the very same mask is drawing the long lines to the right.

Depending on the notes displayed on screen, I get a whole lot of different results like lines, squares, parts of the MC not being covered...

Anyone can tell me what's going on here?

Thanks!