It has always bothered me that animations of raster images are always jerky when they get to the point of animating less than a pixel per frame. Flash assumes that rasters should only live on the exact pixel.
This can be resolved with bitmaps that are created with ActionScript with the Bitmap.pixelSnapping value but for pure animation is a little more complicated.
I’ve just discovered that if you adjust the scale, rotation or skew of the image, Flash will turn pixelSnapping off. So giving a slight degree(more than 0.1%) of one of these factors is the simplest way to demand no pixelSnapping, without requiring one line of ActionScript.