Button disappears on tween

1

i’ve got a function that tweens the _x and _yscale of whatever button is rolled over and a fuction to tween them back, basically grow and shrink the button. the problem is that on rollover the button completely disappears and when i rollout it reappears at the correct “grown” size and then shrinks correctly.

 
for(var b=1;b<=47;b++){ // works on ALL buttons
  _root.map["btn"+b].onRollOver = function()
  {
   var bt:Tween = new Tween(this,"_yscale", Strong.easeOut,this._yscale,this._yscale+1,1.5,true);
   var btn:Tween = new Tween(this,"_xscale", Strong.easeOut,this._xscale,this._xscale+1,1.5,true);
   //trace(this);
   var my_sound:Sound = new Sound();
   my_sound.attachSound("bldg_RO");
   my_sound.start();
  } // end rollover
}// end for loop

any ideas as to why it would disappear?

thanks!