Lost with mx.transition.Tween

just a little frustrating , look at AS



import mx.transitions.Tween;
#include "mc_tween2.as"

MovieClip.prototype.checkMe = function() {
    if (this._currentframe == 6) {
        this.btn.enabled = true;
        this.gotoAndPlay(7);
    }
};

btn_mc3.btn.onRelease = function() {
    gotoAndPlay('gallery')
    _root.bg.gotoAndPlay('gallery')
    _root.my_mc.tween(["_y","_alpha"],[545,0],2)
    var myTween:Tween = new Tween(_root.mc_bg, "_xscale", mx.transitions.easing.Regular.easeOut, _root.mc_bg._xscale, 150, 0.1, true);
    btn_mc3.btn.enabled = false;
    btn_mc4.checkMe();
};
btn_mc4.btn.onRelease = function() {
    gotoAndPlay('contact')
    _root.bg.gotoAndPlay('contact')
    _root.my_mc.tween(["_y","_alpha"],[398,100],2)
    var myTween:Tween = new Tween(_root.my_mc, "_xscale", mx.transitions.easing.Regular.easeOut, _root.my_mc._xscale, 100, 0.1, true);
    btn_mc4.btn.enabled = false;
    btn_mc3.checkMe();
};

the mc_bg is my little bg on stage which on btn press it resizes, the resize tween works great however the btn_mc4 on release doesn’t bring my mc_bg back to 100% am I missing something?