Well, a tad late, but for anyone who'se considering using this, it doesn't really work with simultaneous requests or requests within a close timeframe (e.g. if someone tripple clicked the submit button on a form).
(a) there's no guarantee what order the racing requests will come out of the synchronized blocks and
(b) there's no guarantee that they'll arrive at the server in the order they were submitted! What if the first request's held up by the network and arrives after the others?
Ergo, more often that not, you end up loosing the request spawned by the last click and get presented with a lovely blank page.