Using a toolbar in my view, width % is not working properly 50%+50%!=100%, and when I resize the window, the difference is changing dinamically:

Code:
Ext.Viewport.add({
    items : [
        {
            width : '70%',
            items : [
                {
                    xtype  : 'toolbar',
                    docked : 'top',
                    items  : [
                        {
                            xtype : 'textfield',
                            width : '50%'
                        },
                        {
                            xtype : 'textfield',
                            width : '50%'
                        }
                    ]
                }
            ]
        }
    ]
});
img.png