为什么ext2.0在vista和xp下显示不一样??

vista比xp多了一个横条，感觉是title,但并没有定义title?

var LoginWindow=function(){
    var loginWindow,loginForm;

	createLoginForm=function(){
		loginForm=new Ext.form.FormPanel({
			frame:true,
			labelAlign: 'right',
			labelWidth:75,
			defaultType: 'textfield',
			waitMsgTarget:true,
			items:[{
				fieldLabel: '用户名',
				name: 'operatorName',
				width:100
			},{
				fieldLabel: '密码',
				inputType:'password',
				width:100,
				name: 'password'
			}]			
		});
		loginForm.addButton({
			text: '登录',
			handler: function(){
				loginForm.form.submit({url:'login.do', waitMsg:'登录...'});
			}
		});
		loginForm.addButton({
			text: '重填',
			handler: function(){
				loginForm.form.reset();
			}
		});
	}

	return {
        init : function(){
			var loginLink= Ext.get('loginLink');
			if(loginLink)
				loginLink.on('click',this.showLoginWindow);
			var logoutLink= Ext.get('logoutLink');
			if(logoutLink)
				logoutLink.on('click',logout);
			var inLink= Ext.get('inLink');
			if(inLink)
				inLink.on('click',function(){MainFrame.loadMainFrame('main/main.html');});			
			var homeLink= Ext.get('homeLink');
			if(homeLink)
				homeLink.on('click',function(){location.href=contextPath;});

			createLoginForm();
        },       

        showLoginWindow:function(){
			if(!loginWindow){
				loginWindow=new Ext.Window({
					title:'登录',
					layout:'fit',
					width:260,
					height:135,
					modal:true,
					resizable:false,
					closeAction:'hide',
					plain:true,
					footer:true,
					items:[loginForm]
				});
			}
			loginWindow.show(this);
        }
    };
}();

Ext.onReady(LoginWindow.init,LoginWindow,true);