Internal Computed ReadOnly being overriden

components.example-component.js

import Ember from 'ember';

const { computed, Component } = Ember;

export default Component.extend({
  firstItem: computed.alias('someList.firstObject')
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  someList: [{'foo': 'bar'}],
});

templates.application.hbs

{{example-component
	someList=someList
  firstItem=firstItem
}}

templates.components.example-component.hbs

{{firstItem.foo}}
<button {{action attrs.doSomething}}>Break things</button>

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}