Original:

    displayMenu: function(menu_item) {
        var scrollTop = jQuery(window).scrollTop(),
        elementOffset = menu_item.offset().top,
        distance      = (elementOffset - scrollTop);
        var menu_height = jQuery(window).height() - distance;

        var menu = menu_item.children('ul');

        menu.children('li').eq(0).append('<span class="menu-arrow"></span>');
        jQuery('.menu-arrow', menu).css('top', distance+12);

        menu.css('padding-top', distance);
        menu.height(menu_height);
        menu.show('slide', {direction: 'left'}, 150);
    },



Changed:

    displayMenu: function(menu_item) {
        var scrollTop = jQuery(window).scrollTop(),
        elementOffset = menu_item.offset().top,
        distance      = (elementOffset - scrollTop);
        var menu_height = jQuery(window).height();

        var menu = menu_item.children('ul');

        menu.children('li').eq(0).append('<span class="menu-arrow"></span>');
        jQuery('.menu-arrow', menu).css('top', distance+12);

        //menu.css('padding-top', distance);
        menu.height(menu_height);
        menu.show('slide', {direction: 'left'}, 150);
    },