User sees an error message if they interrupt the autocomplete.js script (and possibly other AJAX routines)

This issue has been reported several times for several projects, but it doesn't appear to have been reported as a core issue yet. Apologies if I've just missed the link.

I have an autocomplete field (like the user or tags autocomplete). If type something in it, and then hit the "submit" button while the AJAX callback is running (eg the blue throbber is throbbing), I get a Javascript popup that says "An HTTP error 0 occurred" followed by the URL of the callback function. According to several reports I've found on the internet (see below), this is a spurious error that, in this particular case, is completely harmless and meaningless. It may also only occur on Firefox, and of course it's easiest to reproduce with either a slow callback or a slow internet connection.

The best solution I've found so far is to find these lines in misc/autocomplete.js:

error: function (xmlhttp) {
alert(Drupal.ahahError(xmlhttp, db.uri));
}

and comment out the call to 'alert.' However, this is a terrible long-term solution, not only because I hack the core but because any legitimate error will now be suppressed as well. Unfortunately, I know very little about javascript and don't know how to distinguish between these two cases.

The desired behaviour, of course, would be that if the *user* interrupts the callback routine, they don't get an alter. But if an error occurs for any other reason, the alert is shown

Other reports:

http://www.mailfunnel.org/development@drupal.org/2008-08/msg00248.html
http://drupal.org/node/211525 (especially comment #13)