The reload-detection mechanism is probably triggered because one of the requests sent by the browser succeeds in updating the session, and the final request compares the session and the submitted value to find that they are identical.

You can't expect that nothing has changed, just because a request is cancelled when the user clicks the submit-button again. The server may be done with the first request by the time it receives the second.

I wouldn't rely on any mechanism to distinguish between the rapid re-submitting of a request and submitting once followed by a reload a while later.