IE9 jquery ui bug

HTML

<a href="#">Click For Dialog</a>

CSS

/*
===>>> IN IE9 - THE CENTER POSITION NOT WORKING 9/20/2013:
*/
 .ui-dialog {
  
}

JavaScript

$(function () {
    $('a').click(function () {
        $('<div>').html('This is a test').dialog({
            position: {
                my: "center",
                at: "center",
                of: window
            }
        });
    });
});