Mouse_over and Mouse_out loop problem

I have a button in my website that has both functions(MOUSE_OVER and MOUSE_OUT), and when i mouse_over in the button it expands its size, but when i mouse_out it’s supposed to change back to it’s original size, except it doens’t.

The code i have is:

aboutb.addEventListener(MouseEvent.MOUSE_OVER, about_anim);

function about_anim (e:MouseEvent) :void{
    aboutb.nextFrame(); //in the next frame is the expanding animation 
aboutb.addEventListener(MouseEvent.MOUSE_OUT, about_anim_out); // to add the mouse_out function


function about_anim_out (e:MouseEvent) :void{

Am i doing anything wrong?