Flash :: Tweening MC Slow Movement With Tweener, Even With Smoothing?

I think that Tweener is not using fractions of pixels on x,y movement, but that exactly what I need. I read about rounded parameter (default:false), that would round pixels, to reduce problems with text, but I want to slowly pan an loaded image, so I don't want to use a rounded value. My code:

var bmp = Bitmap(loader.content);
bmp.smoothing = true;
Tweener.addTween(loader, {x: 20.0, time:10, transition:"linear"});

Image smoothing works fine, but it slides choppy. It looks like moving 1 pixel at seldom frames, not some fraction of px per frame. I'm considering that flash image smoothing has to deal with fraction of pixels. I searched over stackoverflow, and all I could find was about image smoothing, and not about x,y movement smoothing.