Mask

There are 2 movie clips which are used to mask 2 objects. Codes are as follow:
import mx.transitions.Tween;
import mx.transitions.easing.*;
var myTween1:Tween=new Tween(circleClip,"_x",Regular.easeInOut,0,171,3,true);
var myTween2:Tween=new Tween(circleClip1,"_y",Regular.easeInOut,82,267,3,true);
myTween2.stop();
myTween1.onMotionFinished=function(){myTween2.start();}
myTween2.onMotionFinished=function(){myTween1.start();}

When the transitions repeat, the second object suppose to be invisible but it is visible. How to set second object invisible just as it starts from beginning ?