Sencha Architect
Version: 2.1.0 Build 676
Windows 7

Steps to reproduce the error:
  1. Create model, store and proxy* as defined bellow, through architect
  2. Project Inspector > RMB on Users store > Load data
  3. Project Inspector > LMB on Users store 'view response' icon
* I haven't create a reader for my JSON response yet; I changed header values and url for this post

Code:
Ext.define('MyApp.store.Users', {
    extend: 'Ext.data.Store',


    requires: [
        'MyApp.model.User'
    ],


    constructor: function(cfg) {
        var me = this;
        cfg = cfg || {};
        me.callParent([Ext.apply({
            autoLoad: true,
            storeId: 'Users',
            model: 'MyApp.model.User',
            clearOnPageLoad: false,
            clearRemovedOnLoad: false,
            proxy: {
                type: 'rest',
                url: 'example.com/users',
                headers: {
                    Accept: 'application/json;version=1',
                    Authorization: 'basic xpto'
                }
            }
        }, cfg)]);
    }
});


Ext.define('MyApp.model.User', {
    extend: 'Ext.data.Model',


    idProperty: 'key',


    fields: [
        {
            name: 'name'
        },
        {
            name: 'key',
            type: 'int'
        },
        {
            name: 'firstName'
        },
        {
            name: 'lastName'
        }
    ]
});