ActionScript 3.0 :: MouseOver - It Moves Upward Slightly And A Small Amount Of Whitespace Appears At The Top Of The Image?

I'm trying to code a click-and-point adventure game for a class, in which interactive objects glow when you mouse over them.... In the frame I have the background image (in which there is, say, a drawer), and an image of the drawer glowing placed exactly over top of that. The glow image is invisible until you mouse over it, at which point it is supposed to become visible (and disappear upon mouseout). I have the mouseover function linked to the entire glow image (which is a movieclip), but it only seems to work when you mouseover a specific portion of the image (usually a corner). The code looks something like this:

ActionScript Code:
DeskDrawer.addEventListener(MouseEvent.MOUSE_OVER, drawerLightUp);
function drawerLightUp(e:MouseEvent){
DeskDrawer.alpha = 100;
}

when the glow-image is moused over, it moves upward slightly and a small amount of whitespace appears at the top of the image.