ember-data duplicate IDs

adapters.application.js

import Adapter from "ember-data/adapters/rest";

export default Adapter.extend();

application.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  init() {
    this._super(...arguments);
    
    $.mockjax({
      url: '/mocks',
      responseText: {
        "mock": [
        	{
          id: 1,
	        text: "foo"
      	},
        {
          id: 1,
	        text: "second foo"
      	},
        {
          id: 3,
	        text: "bar"
      	}
      	]
      }
    });
  },
  model() {
    return this.store.query('mock', {});
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  
  peek: Ember.computed(function () {
  	return this.store.peekAll('mock');
  })
});

models.mock.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  text: DS.attr('string')
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>

<h2>Query</h2>

<code>
this.store.query('mock', {});
</code>

<ul>
  {{#each model as |mock|}}
    <li>{{mock.id}}: {{mock.text}}</li>
  {{/each}}
</ul>

<h2>Subsequent peek</h2>
<code>
this.store.peekAll('mock');
</code>
<ul>
  {{#each peek as |mock|}}
    <li>{{mock.id}}: {{mock.text}}</li>
  {{/each}}
</ul>

twiddle.json

{
  "version": "0.4.8",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-data": "2.12.1",
    "ember-template-compiler": "2.12.0",
    "jquery-mockjax": "https://cdnjs.cloudflare.com/ajax/libs/jquery-mockjax/1.6.2/jquery.mockjax.js"
  }
}