If you click on a result in Google Instant, the referer sent by your browser to the destination website contains a bunch of parameters, including the all important q=[autocompleted query]
But you're coming from a page whose URL is simply http://www.google.com/ with a bunch of stuff after the # character, i.e. as an on-page anchor.
So the browser appears to be sending a URL as the referer which is different from the URL of the page that you were viewing when you clicked.
There doesn't seem to be an additional redirection, so how on earth do they do that?