Cancel roll out event upon roll over of different clip?

I have MovieClip A on stage, that when the user rolls over it another MovieClip (B) is added above it to the stage (it’s not added as a child of Movieclip A). Now, when the user rolls over this newly added clip, it triggers the roll out event of the clip ‘below’ it. So, how can I prevent this from happening ?

Basically, it’s a movieclip that displays a button when rolled over and hides it when rolled out. I need the roll out NOT to be triggered when the user rolls over movieclip B. Hope this makes sense.

Movieclip B has it’s own event listeners, therefore mouseEnable set to false won’t help here.

A little diagram to help understanding of layout:

Please help me out on this one, I’m really stuck
Thanks in advance for your time