[]这样写的代码，Tween动画里面只有alpha有效果，scalex和scaley没有变化，怎么回事啊？

var sprite:Laya.Sprite = new Laya.Sprite();
sprite.graphics.drawCircle(0, 0, 250, null, "#ff0000", 4);
sprite.graphics.drawCircle(0, 0, 350, null, "#ff0000", 4);
sprite.pivotX = sprite.width * 0.5;
sprite.pivotY = sprite.height * 0.5;
sprite.x = this.width * 0.5;
sprite.y = this.height * 0.5;
this.addChild(sprite); 
Laya.Tween.to(sprite, {scaleX:1.5, scaleY:1.5, alpha:0}, 5000);