Why can't the stage hear the mouse up?

[na_il]

import flash.events.MouseEvent;

stage.addEventListener(MouseEvent.MOUSE_DOWN, slider_over);

function slider_over(evtObj:MouseEvent){
//slider.startDrag();
trace(“im cool”);
}

stage.removeEventListener(MouseEvent.MOUSE_UP, slider_over_up);

function slider_over_up(evtObj:MouseEvent){
//slider.stopDrag();
trace(“im smart”);
}