ActionScript 3.0 :: Function Not Fire Unless Mouse Clicked?

My document class is Controller It's constructor addChilds an instance of MenuScreen

MenuScreen has 1 button called 'gallery'. Clicking on it removes the MenuScreen from the document class and adds galleryScreen to the Document class.

After the galleryScreen becomes a child of the document class I add a keyevent listener like so:

ActionScript Code:
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
Here's a snippet of keyDownHandler:
ActionScript Code:
public function keyDownHandler(event:KeyboardEvent):void{

[Code]....

The Problem is: 1) I'm pressing LEFT arrow key like mad and nothing happens UNTIL I left click anywhere on the screen, THEN keyDownHandler works.