Ember unloadRecord doesn't remove observers

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle'
});

application.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  beforeModel: function() {
  	this.store.push({
      data: {
        type: 'event',
        id: 1,
        attributes: {
          name: 'test',
        }
      }
    });
  },
  model: function() {
    return this.store.peekAll('event');
  },
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
A model should show here for 5 seconds and then disappear. However even after the model is destroyed the observer stays attached as you can see in the console:
<br>
<br>
{{#each model as |item|}}
  {{item.name}}, dies at age {{item.ticks}} seconds
{{/each}}
<br>
<br>

clock.service.js

import Ember from 'ember';

export default Ember.Service.extend({
  init: function() {
    var self = this;
    console.log('clock started');
    window.setInterval(function() {
      self.incrementProperty('tick');
    }, 1000);
  },
});

models.event.js

import DS from 'ember-data';

export default DS.Model.extend({
  clock: Ember.inject.service(),
  name: DS.attr(),
  ticks: Ember.computed('clock.tick', function() {
    return this.get('clock.tick');
  }),
  
  // this is a way of removing stale models after a certain time period has passed
  aging: Ember.observer('clock.tick', function() {
    console.log(this.get('clock.tick'));
    if (this.get('clock.tick') > 5) {
      // manually removing observer fixes the issue
      // this.removeObserver('clock.tick');
      this.unloadRecord(this);
      console.log('record unloaded, observer should stop now');
    }
  }),
});

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "canary",
    "ember-data": "canary",
    "ember-template-compiler": "canary"
  }
}