Can't use 'rows' in a cells item of 'tabview'

i can’t use ‘rows’ property in a ‘cells’ item of ‘tabview’, why?
is it a bug?
see: http://webix.com/snippet/a7e2e85c

<code class="js">
//Uncaught TypeError: Cannot read property '0' of undefined webix_debug.js:4887
webix.ui({
  rows:[
    { id: 'tabs',
      view: 'tabview',
      tabbar: {
        optionWidth:200, 
        close:true, 
        value:'module1',
        on:{
          onAfterRender : webix.once(function(){
              $$(this.config.value).show(false, false);
          })
        }
      }, 
      cells:[
        {id: 'tab_index', header: 'index', body:{id:'index', template:'index.'}},
        {id: 'tab_module1', header: 'string',
          body:{ //here, can't use 'rows',why? is it a bug?
            id:'module1', 
            rows:[
              {template:'top'},
              {template:'bottom'}
            ]
          }
        }
      ]
    }
  ]
});
`

The issue is caused by your onAfterRender handler. It calls show method for layout that is not rendered yet (your onAfterRender is fired for tabbar only). Try to call show() method from delay:

http://webix.com/snippet/2d5a6cb6

thanks a lot! I resolved this problem in this way: http://webix.com/snippet/c9fee7b0