Store returns ProxyObject when Model.reopen() is called

I would like to reopen Model class. Should be easy, so:

// app/app.js
import Ember from 'ember';
import Resolver from './resolver';
import loadInitializers from 'ember/load-initializers';
import config from './config/environment';
import DS from 'ember-data';

After this this.get('store').findRecord('example', 1) resolves into ProxyObject in controller. This happens only on first page load after F5 it is ok (it resolves into record as it should).

I already asked on stackoverflow but no success.