When the browser makes an AJAX call (form submission, button press, etc) in a high latency situation, it is entirely possible that the request may timeout and the browser will have to retry. This is handled in the browser by handling failure on the jQuery AJAX request. Unfortunately, the server-side component of Lift's AJAX has no awareness of the retry mechanism. As such, a retry can potentially lead to repeated invocations of the AJAX handler function. Considering that the retry mechanism itself is something handled internally by Lift, I would expect that the application layer would be completely shielded from any associated semantic effects.

I propose that every AJAX request should get a once-use identifier. Retries would use the same id as the original, but all other requests would get a unique id. This would allow the server to differentiate repeated AJAX requests from retries, giving it the ability to ensure that AJAX handler functions are only invoked once per request.

See discussion here: http://groups.google.com/group/liftweb/browse_thread/thread/5b8d430dcea70776