Bizarre Behavior testing ember with simple auth

I am writing my first ever ember tests. I am using ember-cli and ember 1.13.6 with simple-auth 0.8.0

I am seeing some baffling behavior while running my tests in headless mode with phantom.js

The odd behavior seems to occur when I chain multiple andThen() statements. In my app, if a user is not authenticated, all route transitions should redirect to /login. Right now this happens during the first andThen() of a given test but any transitions in a following andThen() will allow unauthenticated users through to a restricted route

eg:

test('unauthenticated', function(assert) {
  assert.expect(1);
  visit('/maps');

  andThen(function() {
    assert.equal(currentURL(), '/login', "viewing authenticated routes while unauthenticated redirects to login");
  //this test passes
  });

  visit('/maps');

  andThen(function() {
    assert.equal(currentURL(), '/login', "viewing authenticated routes while unauthenticated redirects to login");
  //this test fails
  });
});

Although the app does seem to be somewhat aware of simple auth because this all passes:

test('unauthenticated', function(assert) {
  assert.expect(1);
  visit('/maps');

  andThen(function() {
    assert.equal(currentURL(), '/login', "viewing authenticated routes while unauthenticated redirects to login");
  });
});

test('authenticated', function(assert) {
  assert.expect(1);

  authenticateSession();
  visit('/maps');

  andThen(function() {
    assert.equal(currentURL(), '/maps', "able to view authenticated route after authenticating");
  });
});

A final weird behavior I'm seeing is that authenticateSession() works when called before the first andThen as in the previous example but fails with the error ReferenceError: Can't find variable: Promise if called after the first andThen() like:

test('unauthenticated', function(assert) {
  assert.expect(1);
  visit('/maps');

  andThen(function() {
    assert.equal(currentURL(), '/login', "viewing authenticated routes while unauthenticated redirects to login");
  });

  authenticateSession();
});