[jQuery] IE6 .hover() problem

I fixed the missing CSS :hoverfunction for my navigation via jQuery.
If I hover ofer a list item everything is displayed correctly but if I
hover out the 'span_ie_hover' class won't be removed.. I could cry :(

        //if the user uses IE6 or less
        if ($.browser.msie && $.browser.version.substr(0,1)<7) {
                $('#navigation li').hover(
                function() {
                  $(this).children('a').addClass('li_ie_hover png_bg').children
('span').addClass('span_ie_hover png_bg'); // This works fine
                },
                function() {
                  $(this).children('a').removeClass('li_ie_hover 
png_bg').children
('span').removeClass('span_ie_hover png_bg'); // But this doesn't work
                });
        };