cursor stops movie clip buttons

I have animated movie clips as buttons. When the animation reaches the point where the cursor sits on the button it vanishes. Here is the script I have on the main time line:

//news_mc is the instance name of my movie clip button

news_mc.addEventListener(MouseEvent.CLICK, newsPage);
news_mc.addEventListener(MouseEvent.MOUSE_OVER, newsRollOn);
news_mc.addEventListener(MouseEvent.MOUSE_OUT, newsRollOff);
news_mc.buttonMode = true;
function newsRollOn(event:MouseEvent):void {
news_mc.gotoAndPlay("in");
}

function newsRollOff(event:MouseEvent):void {
news_mc.gotoAndPlay("out");
}

function newsPage(event:MouseEvent):void {
gotoAndStop("news");

I know there is something about
news_mc.mask = ??? I'm not sure if I sure what part of the mask I use. I have a layer that has the button background (instance name - background) and then the 2 layers that form the animated mask - the mask layer contains a copy of the button background (instance name - background2) and then the animated later of the mask contains a gradient that slides over the button (instance name - masker).

What is happening?