bug rendering frozen objects

controllers.application.js

import Ember from 'ember';

const Thing = Ember.Object.extend({
  label: null,
});

function makeItems() {
  return Ember.A([
    Thing.create({label: 'One'}),
    Thing.create({label: 'Two'}),
    Thing.create({label: 'Three'}),
  ]);
}

export default Ember.Controller.extend({
  frozenItems: makeItems().map(item => Object.freeze(item)),
  thawedItems: makeItems(),
});

templates.application.hbs

<h1>Error rendering object frozen with `Object.freeze`</h1>

<p>See <a href="https://embercommunity.slack.com/archives/C04EZF6GV/p1491258796822785">Slack discussion</a></p>

<p>Thawed (not-frozen) items</p>
<ul>
{{#each thawedItems as |item|}}
<li>Item: {{item.label}}</li>
{{else}}
<li>There were no items</li>
{{/each}}
</ul>

<p>Frozen items (should print the same thing as the thawed items). If nothing displays, there is a bug.</p>
<ul>
{{#each frozenItems as |item|}}
<li>Preset: {{item.label}}</li>
{{else}}
<li>There were no items</li>
{{/each}}
</ul>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}