Well that actually answers the question... Lots of functions in jquery won't work for things that have display:none in the CSS.... since they technically have no size when they aren't displayed, then it can't resize them effectively.
One solution I can think of is to use jquery to add mouseover events to each of the menu <li> elements that call the window resize event so that it will re-calculate and resize the menu items as they are displayed.
I haven't tested, but it might look something like:
<script>
$( document ).ready(function() {
$('#cssmw0').find('li').each(function() {
$(this).mouseover( function() {
$(window).resize();
});
});
});
</script>