showModalDialog causes path problems for IE

Question

My master page loads script files like:

<script src="/Scripts/jquery-1.4.1.js" type="text/javascript"></script>

Elsewhere I have a function that pops up a modal dialog box using this masterpage in the form:

function openCreateUserPopup(URL) {
    page = window.showModalDialog(URL, 'UserEditor', "dialogwidth: 450px; dialogheight: 370px; center: yes; resizable: yes");
    $("#Step1Register").submit();
}

FF works fine. IE tosses a file not found for each of my .JS files included in the above fashion. However...even though IE reports a file not found it _has, in fact, found and loaded the file - all the jQuery stuff works.

The problem is the ShowModalDialog command - things work correctly if i open the popup with a plain old:

page = window.open(URL, 'Editor', 'toolbar=0,scrollbars=1,location=0,statusbar=0,menubar=0,resizable=1,width=600,height=400');