During and after the animation of the animated gif, the parent's block background-image should become visible, viewable through the animated gif's transparency.
Original testpage where such buggy behavior can be seen: Transparency of animated GIF when repeated (repeat-x or repeat-y) in a background fails and shows as a black cover.
Original bug as reported by ahacks.com web developer: IE8 bug lingers
Firefox 3.5, Opera 9.64, Safari 4.0, Konqueror 4.2.4 and NS 7.2 pass this test.