Created attachment 125498 [details] Test case Consider the following: * A block, let's call it container is positioned relatively. * Inside it, we center horizontally another block using auto margins. * We set padding-right on the container to a positive value * The inner block is expected to shift to the left. It does not in WebKit. The error is present in the r106740 nightly build of WebKit and in Chromium 16.0.912.77. Firefox displays the inner block shifted to the left as expected. The bug does not happen when changing padding-left. Attached is a test case. For your convenience I hosted it on a web server here: http://epsy.net46.net/stuff/webkit-margins-not-updating.html If your browser/window manager allows it, you can try switching to the inspector while hovering. The inner box updates to the correct position if you change the selection in the Elements tab. Another workaround I found was to also set a margin. Setting padding-left instead has no other effect than its own.
Confirmed present in Chrome 19.0.1035.0 canary
Just thought I'd add another live test-case for this since we're running into it: http://jsfiddle.net/YFGyp/5/
I can't reproduce this on trunk. Comment or re-open if you're still seeing this issue.