Drag 'n overlap: attachmovie clip once

Hello all Kirupians!

In the attached file I’m working on two balls, a yellow and a grey one. they can be dragged and dropped. When they’re overlapping, a menu is attached.

Now the problem: The menu I attached keeps on getting attached, instead of one menu I see a lot of them. I’ve used a bitmapdata function instead of a hittest function and the ball get the attachmovieclip function in the On enter Frame.

What am I doing wrong here? files can be downloaded at :

the swf
the fla

As you can see, [COLOR=Magenta]when you keep draggin the yellow ball inside the grey one, the menu keeps being attached.[/COLOR] how can I make sure it can only be attached once?