[development] autocomplete.js and http error 0

I'm working with an autocomplete text field in a module, and some users were getting an alert error, "An HTTP error 0 occured". I was finally able to reproduce this error, not only on my form but on a standard CCK form as well; if you click the form submit button while the autocomplete is retrieving entries (the 'blue wheel' is present), it triggers the error. Surprisingly, I couldn't find a lot of info on a drupal search, though I did see some related reports in other projects. Looking at the autocomplete.js file, I see the alert at line 285. Obviously I can change it here, but always hate to hack the core. Any ideas? Regards, Roger