Editing cached value of new computed array

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  things: [1, 2, 3],
  computedArray: Ember.computed('things.[]', function() {
    return Ember.A(this.get('things').slice());
  }),
  actions: {
    pushToComputed() {
      this.get('computedArray').pushObject('wombat');
    },
    pushToThings() {
      this.get('things').pushObject(4);
    }
  }
});

templates.application.hbs

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

<h2>Original</h2>
{{#each things as |thing|}}
	{{thing}}<br>
{{/each}}

<h2>Computed</h2>
{{#each computedArray as |thing|}}
  {{thing}}<br>
{{/each}}

<button onclick={{action 'pushToComputed'}}>computed</button>
<button onclick={{action 'pushToThings'}}>things</button>

<br>
<br>

twiddle.json

{
  "version": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}