在ie8下ext显示的有关问题 _Ajax

在ie8下ext显示的问题
在ie8下，点击左边的树形导航栏，在右面板中，弹出相对应的内容，这些内容都写在iframe中，但是在ie8下，需要随便在页面上点击一下鼠标，才能显示内容，换成Firefox和ie7，都能正常的显示，求各位高手解答。
这是部分代码
HTML code
<%@ page contentType="text/html;charset=UTF-8"%>
<%@ include file = "/includes/jsp/init.jsp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>系统首页</title>

<!-- 引入基础的JS和CSS文件 -->
<%@ include file="/common/meta_ext.jsp"%>
<link href="/resources/css/index/index.css" rel="stylesheet" type="text/css"/>
<link href="/resources/css/index/index-treetab.css" rel="stylesheet" type="text/css"/>
<script src="/resources/js/index/index.js" type="text/javascript"></script>

<script src="/resources/js/ext/ux/Portal.js" type="text/javascript"></script>
<script src="/resources/js/ext/ux/PortalColumn.js" type="text/javascript"></script>
<script src="/resources/js/ext/ux/Portlet.js" type="text/javascript"></script>

<script src="/resources/js/ext/ux/TabCloseMenu.js" type="text/javascript"></script>
<script src="/resources/js/jquery/jquery.js" type="text/javascript"></script>
<script type="text/javascript">
var opername='<%= user.getOperName()%>';
Ext.onReady(function(){
    Ext.QuickTips.init();
    //定义页头
    var header = new Ext.Panel({
        border: false,
        layout: 'anchor',
        region: 'north',
        margins: '0 0 1 0',
        height: 100,
        items: [{
            xtype: 'box',
            el: 'header',
            border: false,
            anchor: 'none -1'
        }],
        bbar: [
            '->','-',{
                xtype: 'splitbutton',
                text: '当前用户：'+opername,
                iconCls: 'icon-user-male',
                menu: [{
                    text:'修改用户基本信息', handler:help
                },{
                    text:'修改密码', handler:help
                }]
            },'-',{
                text: '退出系统',
                iconCls: 'icon-exit',
                handler: relogin
            },'-']
    });
    
    //定义树菜单控件
    var tree = new Ext.tree.TreePanel({
        useArrows: true,
        animate: true,
        enableDD: false,
        border: false,
        rootVisible: false,
        autoScroll: true,
        containerScroll: true,
        bodyStyle: 'padding:3px',
        root: new Ext.tree.AsyncTreeNode({
            id: '-1',
            draggable: false,
            leaf: false
        }),
        loader: new Ext.tree.TreeLoader({
            dataUrl: '/extAction.do?task=getTreeJson',
            listeners: {
                "beforeload": function(treeLoader, node){
                    treeLoader.baseParams.id = node.id;
                }
            }
        })
    });

    tree.on('click', function(node, e){
        if(node.id != -1 && node.attributes.url != null){
            openUrl(node.attributes.url);
        }else{
            tree.expandPath(node.getPath());
        }
    });
    tree.on('beforeexpandnode', function(node){
            if(node.id!=-1&&node.getDepth()==1){
                tree.collapseAll();
            }
    });
    

    //定义树菜单面板
    var treePanel = new Ext.Panel({
        region: 'west',
        collapsible: true,
        autoScroll: true,
        split: true,
        iconCls: 'icon-expand-all',
        title: '菜单导航',
        width: 220,
        maxWidth: 300,
        minWidth: 220,
        margins: '0 0 3 5',
        items: tree
    });
    
    
    
    //定义主界面整体布局
    var viewPort = new Ext.Viewport({
        layout: 'border',            
        items: [header, treePanel, new Ext.Panel({
                id:'main_panel',
                region: 'center',
                width:400, 
                contentEl:'con'     

                })]
    });
     
});

function openUrl(url){
       if(url!=null){
        document.getElementById('misFrame').src = url;
       }
}
    
    
</script>

</head>
<body>
    <div id="header" style="background-image:url(/resources/images/background/header6.jpg);background-repeat: repeat-x;" >
        <img   src="/resources/images/background/toplf5.jpg" />
    </div>
    <div id="con" style="height:100%;" >
        <iframe src="http://www.baidu.com" id="misFrame"  name="misFrame" width="100%" height="100%" frameborder="0"></iframe>
       </div>
</body>
</html>