Cannot read property 'internalId' of undefined

Hi everyone,

I have a problem with Ext JS 4.1 Tree panel. I use a tree with a static store and attach a dynamically loaded node with it's store to initial tree as a child.

Here is the working example (I've found this example in the net and customized for my application):

Code:

Ext.define('demo.UserModel', {
    extend: 'Ext.data.Model',
    fields: ['text', 'cls']
});


var userTreeStore = Ext.create('Ext.data.TreeStore', {
    model: 'demo.UserModel',
    proxy: {
        type: 'ajax',
        url : '/users.php',
        reader: {
            type: 'json',
            root: 'users'
        },
        pageParam: undefined,
        startParam: undefined,
        limitParam: undefined,
        listeners: {
            append: function() {
                // custom icon processing goes here based on 'cls' property
            }
        }
    }
});


userTreeStore.setRootNode({
    text: 'Users',
    id: 'users',
    leaf: false,
    expanded: false
});


var settingsTreeStore = Ext.create('Ext.data.TreeStore', {
    root: {
        expanded: true,
        children: [
            {
                text: 'Settings',
                leaf: false,
                expanded: true,
                children: [
                    {
                        text: 'System Settings',
                        leaf: true
                    },
                    {
                        text: 'Appearance',
                        leaf: true
                    },
                    {
                        text: 'Appearance',
                        leaf: true
                    },
                    {
                        text: 'Appearance',
                        leaf: true
                    },
                    {
                        text: 'Appearance',
                        leaf: true
                    }]
            }]
    }
});


settingsTreeStore.getRootNode().getChildAt(0).insertChild(2, userTreeStore.getRootNode()).expand();


Ext.onReady(function() {
Ext.create('Ext.tree.Panel', {
    title: 'Panel',
    renderTo: Ext.getBody(),
    height: 300,
    width: 300,
    store: settingsTreeStore,
    rootVisible: false,
    listeners: {
        itemclick: function(view, row, node, index, e) {
            if(row.get('text') === 'Users') {
                userTreeStore.load();
            }
        },
        afterrender: function(tree) {
            tree.getSelectionModel().select(tree.getStore().getRootNode().firstChild);
        }
    }
});
});

The url above returns one level nested data like this:

{users: [{"id": "user1", "text": "User1", "cls": "file"}, {"id": "users1", "text": "Users1", "cls": "folder"}]}

When I run this example and expand/collapse the dynamic Users node several times, I get the following js error:

TypeError: Cannot read property 'internalId' of undefined.

ext-all-debug.js updateIndexes method of Ext.view.AbstractView.

I don't have any duplicates in my data, it is correct. I have reviewed previous posts regarding this error but no fix was available.

Could you please look at this issue and provide a quick fix if it is possible?

Thanks in advance.

Cannot read property 'internalId' of undefined