问jQuery mouseenter - mouseleave的怪癖

EN

$(function(){
  //bind event
  $("li.level1").mouseenter(   
    function(){
       // make sure the item would diplay
       $(this).find("ul:first").find("li.level2").show(); 
       // do "show" 
       $(this).find("ul:first").show(500);       
    });

  $("li.level1").mouseleave(
      function() {
        // do "hide" 
        $(this).find(":parent").hide(500);
      }
  );
});