TweenEvent.MOTION_COMPLETE not firing

[misterQ]

My tween always runs but sometimes doesn't fire MOTION_COMPLETE.

movement(targetMC1);
movement(targetMC2);
mo...

function movement(object:Object):void{
var twn:Tween = new Tween(object, ...);
twn.addEventListener(TweenEvent.MOTION_COMPLETE, motComp);
}

function motComp(e:Event):void{
doOtherStuff()
}

Is there something wrong with this?