Config Proprety in Extjs-6 Picker doese not work perfectly - extjs

Question

I'm developing an application using Extjs-6. I extend a viewclass from a Ext.form.field.Picker as follow:
Ext.define('Fiddle.MyCombo', function(){
var me;
var initComponent = function()
{
me = this;
Ext.apply(me, {});
me.callParent(arguments);
};
var createPicker = function ()
{
var textfield = {
xtype: 'textfield',
width: '100%',
border: false,
listeners: {
change: function(component, newValue)
{
me.setStr(newValue);
}
}
};
var panel = new Ext.panel.Panel({
rtl: true,
minWidth: 300,
floating: true,
items: [textfield]
});
Ext.Msg.alert('Attension', 'Init Value is : ' + me.getStr());
return Ext.widget(panel);
};
return {
extend: 'Ext.form.field.Picker',
alias: 'widget.mycombo',
initComponent: initComponent,
createPicker: createPicker,
config: {
str: ''
}
};
});
I use this class as follow:
Ext.define('Fiddle.Main', {
extend: 'Ext.panel.Panel',
width: 400,
height: 200,
title: 'Its me!',
items: [{
xtype: 'mycombo',
name: 'item1'
}, {
xtype: 'mycombo',
name: 'item2'
}]
});
When I open first mycombo(item1) and type some word in textfield input, and then open second mycombo item(items2), in createPicker function I alert str value of item, and it show the item1's value.
Why it show item1's str value?
Where is wrong?
My Sample fiddle is here.