Thumbnail tween getting garbage collected

I recently posted on here about tweening in alphas of thumbnails that I was adding to a movieclip. It seems that the tween is getting garbage collected because not all of the thumbs fade in all the way. I have the tween defined outside of the function, but it is tweening a loader that is created within the function. Could this cause the tween to get garbage collected? if so, how do I fix it?

Here is the pertinent code:

var thumbTween:Tween;
var my_thumb:Loader;

function thumbLoaded(e:Event):void{
my_thumb = Loader(e.currentTarget.loader);
my_thumb.alpha = 0;
container_mc.addChild(my_thumb);
thumbTween = new Tween(my_thumb, “alpha”, None.easeNone, 0, 1, 1, true);
}

Any ideas?
thanks