form submits multiple times in IE only at customer site

We have a customer using our application that has a problem.
Within our app, we have a two different forms (one generates
an email, the other a fax via a webservice). When they click the
submit button, IE6 is generating the event 6 times!!! So they
end up sending 6 faxes or 6 emails. We simply cannot reproduce
this. We can't find anything wrong in our code that might cause
this, I can't find anything in MS Technet about IE bugs that
might cause this (and in any case we cant repro it in IE).
It's not the customer clicking something 6 times.

The code that submits the form is very simple:

<script>
function submitEmail() {
if(confirm("Are you sure you want to send this email?")) {
document.getElementById('emailForm').submit();
window.close();
}
}

We're stumped. Has anyone encountered anything like this? I have them
installing Firefox on a test machine to see if it's IE specific but
regardless
we need to resolve this for IE since that's the platform the company is
standardized on.




.