A blue box has fixed dimensions, overflow:auto, a non-repeating background image (green, with some black lines in the top part) of the same height as the box itself. A taller child causes a vertical scrollbar. While scrolling in IE8 the background image wrongly moves 1px up and down (this can be seen looking at the black lines of the image, and at the blue background appearing either at the bottom or at the top of the image). Something above the box (even a simple top margin) seems necessary to trigger the problem.