一个问题?tabpanel中放checkbox不能正常显示

今天写了一个tabpanel里面放checkbox不能正常显示，改变一下窗口大小才显示出来,我设置的高度也应该够呀








代码
var authtabpanel = new Ext.TabPanel({
        activeTab: 0,
        renderTo:'roleauthpanel',
        frame:true,
        defaults:{autoHeight: true},
        items:[
       
       
        {title:'strategyInfo',height:300,items:[
        {xtype:'checkbox',height:100,boxLabel: 'Item 3', name: 'cb-auto-3',inputValue:'item3'}
        ]}
        ,
       
        {title:'systemInfo',height:300,items:[
        {xtype:'checkbox',height:100,boxLabel: 'Item 3', name: 'cb-auto-3',inputValue:'item3'}
        ]}
        ,
       
        {title:'baseInfo',height:300,items:[
        {xtype:'checkbox',height:100,boxLabel: 'Item 3', name: 'cb-auto-3',inputValue:'item3'}
        ]}
       
        ]
        });