TabPanel within a Panel does not work properly

I have a basic example below, works in other browsers but does not work on my iPhone 6 Plus. I do not know if in another iPhone the same problem occurs.

When do my TabPanel the root it works, but as a child, does not appear the Toolbar.

Code:

Ext.define("AppTest.view.MainView", {
    extend: "Ext.Panel",


    config: {
        layout: 'fit',
        items: [
            {
                xtype: 'tabpanel',
                tabBar: {
                    docked: 'bottom',
                    layout: {
                        pack: 'center'
                    }
                },


                defaults: {
                    styleHtmlContent: true
                },


                items: [
                    {
                        title: 'Home',
                        iconCls: 'home',
                        html: 'Home Screen'
                    },
                    {
                        title: 'Contact',
                        iconCls: 'user',
                        html: 'Contact Screen'
                    }
                ]
            }
        ]
    }
});

Ext.application({

    views: [
        'MainView'
    ],
    name: 'AppTest',
    launch: function () {
        Ext.create('AppTest.view.MainView', { fullscreen: true });
    }


});

Is it a bug? Or something I'm doing wrong?

Thanks in advance.

TabPanel within a Panel does not work properly