These are the steps i've been using. Probably reproducible using the mouse as well? Let the page render after each step. Load acid2 and let it render. Press command-minus twice to zoom out Reload the page using command-r Press command-0 to zoom back to normal Reload the page using command-r Now no longer renders correctly and is persistently broken over reloads. I've had it fail in 2 different ways so far. Not entirely sure what the difference between the 2 failure modes was.
Created attachment 21835 [details] Example of broken acid2 rendering after zooming out and back in again
As far as I understand, the going directly to #top is not a correct way to run Acid2. The persistent change in rendering certainly does look wrong, but I'm still not quite sure if it's a bug.
"Note: When taking the test, you should use the default settings of the browser you are testing. Changing the zoom level, minimum font size, applying a fit-to-width algorithm, or making other changes may alter the rendition of the Acid2 page without this constituting a failure in compliance." [http://www.webstandards.org/action/acid2/guide/] The test always should be performed by going to http://acid2.acidtests.org/ first and clicking "Take the Acid 2 test". It's important for proper calculation of position: fixed "hat". I close the bug report since the described issue is not a bug.