Why is Model.getAssociatedData() empty

[besogon]

I defined 2 models.

Ext.define('EventType', {
    extend: 'Ext.data.Model',


    idProperty: 'eventTypeId',


    fields: [
        {name: 'eventTypeId'}
    ]
});

Ext.define('Event', {
    extend: 'Ext.data.Model',


    idProperty: 'eventId',


    fields: [
        {name: 'eventId'},
        {
            name: 'eventTypeId',
           type: 'string',
           reference: {
               type: 'EventType',
               role: 'EventType',
               association: 'EventsByType',
               inverse: 'events'
           }
       },
   ]
});

Then I filled store 'EventType' with data:

[                {eventTypeId: 'A'},
                {eventTypeId: 'B'},
                {eventTypeId: 'C'}
            ]

and store 'Events'

[
                {eventId:1, eventTypeId: 'A'},
                {eventId:2, eventTypeId: 'A'},
                {eventId:3,eventTypeId: 'C'}
            ]

Here is the example
https://fiddle.sencha.com/#view/editor&fiddle/31gm

Result:
Model.getAssociatedData() => empty object
Model.getEventType() => correct Model

So.. the question: why?? Is it a bug or intended behavior?
If this is not a bug then when getAssociatedData() should not be empty?