jQuery problem with Safari

Can anyone shed some light on why this works in Firefox but not in Safari? You can see the problem here: http://www.thechangestudio.com/index2.php

Thanks

<script type="text/javascript">

$(document).ready(function() {

    $("ul#topnav li").hover(
    function() { 
        $(this).find("span").stop(true, true).slideDown(1000); 
        return false; 
        }, function() { 
            $(this).find("span").slideUp(500); 
            ret开发者_如何学编程urn false;
        });
    }); 

</script>

Webkit browsers (Safari, Chrome) and Opera will only animate span elements in certain positions within the parent element. Use a different element for your animation such as a div or an anchor.