It has to do with pushState() being called in the head.

from IRC:
rgrove Chrome's popstate behavior does differ from other browsers, but this is a new wrinkle I hadn't seen before. Hmm.
rgrove Actually, the bug occurs with the code in the body too, but not if you wait until after window.onload.
rgrove Basically if you call pushState before the first popstate event for the pageview (and Chrome always fires one, whereas other browsers only fire for pushState pageviews), then the bug occurs.

part 2:
Race condition.
rgrove The popstate event doesn't actually include any information on the new URL, so we have to manually inspect window.location to figure out what the URL has changed to. Unfortunately,
window.location isn't guaranteed to be updated before popstate fires, so we have to use an async timeout to inspect the location *after* the popstate event (and everything else in the event queue) are
finished...

Ref url http://jsfiddle.net/triptych/zpLNe/