'this' undefined only from component integration test

This is an Ember component that will need this at some point:

export default Component.extend({
  filteredSubs: computed.filter('model.subs', function() {
    // this will always return true in development http://localhost:4200/dummy
    // but will always return false in test because this === undefined
    return this;
  })
});

Dummy has a one-to-many relationship to Sub:

export default Model.extend({
  subs: hasMany('sub')
});

export default Model.extend({
  dummy: belongsTo('dummy')
});

This test fails but shouldn't:

test('it renders', function(assert) {
  let dummy = server.create('dummy');
  server.create('sub', { dummy });

  this.set('dummy', dummy);
  this.render(hbs``);

  assert.equal(this.$().text().trim(), 'Hi! There are 1 sub-dummies');
});

not ok 13 Chrome 63.0 - Integration | Component | show dummy: it renders

actual: Hi! There are 0 sub-dummies

expected: Hi! There are 1 sub-dummies

• Not sure if this could be an Ember bug or ember-cli-mirage bug,
• I have isolated the issue in a fresh repo https://github.com/stephanebruckert/ember-bug-16052
• Also posted on https://github.com/emberjs/ember.js/issues/16052