ActionScript 3.0 :: Bug Using Tween MOTION_FINISH Event?

I programming a game and when i destroy an enemie, i wan't the game to create a textfield with the enemie's points value that moves and disapears after a while.So when the enemie is destroyed, i create the textfield and ad a tween. Then i ad an eventListener to the tween so the textfield is destroyed when the tween is completed.

Code:
var points:TextField = new TextField;
var tween:Tween = new Tween(points,"y",Strong.easeOut,points.y,points.y-30,0.5,true);tween.addEventListener(TweenEvent.MOTION_FINISH,delete_txt);
addChild(points);

Then the function that deletes the textfield :

Code:
protected function delete_txt(e:Event)
{
removeChild(e.target.obj);e.target.removeEventListener(TweenEvent.MOTION_FINISH,delete_txt);
}

It does work most of the time but like once in 20-30 times the textfield doesn't disapear and just stays in the air. I placed a trace in the delete_txt function and the program doesn't seem to get to it when the bug occurs.I'm not getting any error.