I think this is javascript-related, but I'm not sure. On this website you can navigate posts by using the up/down arrows and you can navigate pages (forward/back) using the left/right arrows (see the top right of the page for explanation). The left/right functionality works, but the up/down does not anymore. I just noticed this in the r40957 build from 2009-02-13.
Confirmed as a regression with r41016.
<rdar://problem/6589657>
The problem here is with a broken getBoundingClientRect implementation, which jQuery decides to use when available. Try e.g. javascript:alert(document.getElementById("drop7").getBoundingClientRect().top)
Created attachment 28728 [details] patch
Fixed in r41811.