Code:
Ext.define('common.Connection', {
    singleton: true,
    
    mixins: {
        observable: 'Ext.util.Observable'
    },
    
    socket: null,
    
    constructor: function() {
        this.addEvents(['offline','connecting', 'online']); 
        
        Ext.onReady(Ext.bind(function() {
            this.fireEvent('connecting');


            this.socket = io.connect(null); 
            this.socket.on('error', Ext.bind(this.onError, this));
        }, this));
    },


    onError: function(reason) {
        this.fireEvent('offline', reason);
    }
});
This code worked perfectly in ExtJS 4.0.7, 4.1b1 and 4.1b2, but fails on ExtJS 4.1b3 in Observable.js line 444.

Adding "hasListeners: {}" into class fixes it and everything seems working.

A bug?