Timezone issue after upgrading to Django 1.9

Question

I have a test in Django 1.8.5, which passes. Here is is

def test_user_returns_from_vacation_correctly_increments_review_timestamps(self):
        self.user.profile.on_vacation = True

        now = timezone.now()
        an_hour_ago = now - timedelta(hours=1)
        two_hours_ago = now - timedelta(hours=2)

        self.user.profile.vacation_date = an_hour_ago
        self.user.profile.save()
        self.review.last_studied = two_hours_ago
        self.review.save()
        previously_studied = self.review.last_studied

        user_returns_from_vacation(self.user)
        rev = UserSpecific.objects.get(id=self.review.id) #<---This is the line causing the error!
        print(rev)
        self.assertNotEqual(rev.last_studied, previously_studied)
        self.assertAlmostEqual(rev.last_studied, an_hour_ago, delta=timedelta(seconds=1))

However upon upgrading to Django 1.9 this test causes this error:

Error
Traceback (most recent call last):
/pytz/tzinfo.py", line 304, in localize
etc etc
    raise ValueError('Not naive datetime (tzinfo is already set)')
ValueError: Not naive datetime (tzinfo is already set)

Here is the related user_returns_from_vacation code:

def user_returns_from_vacation(user):
    """
    Called when a user disables vacation mode. A one-time pass through their reviews in order to correct their last_studied_date, and quickly run an SRS run to determine which reviews currently need to be looked at.
    """
    logger.info("{} has returned from vacation!".format(user.username))
    vacation_date = user.profile.vacation_date
    if vacation_date:
        users_reviews = UserSpecific.objects.filter(user=user)
        elapsed_vacation_time = timezone.now() - vacation_date
        logger.info("User {} has been gone for timedelta: {}".format(user.username, str(elapsed_vacation_time)))
        updated_count = users_reviews.update(last_studied=F('last_studied') + elapsed_vacation_time)
        users_reviews.update(next_review_date=F('next_review_date') + elapsed_vacation_time)
        logger.info("brought {} reviews out of hibernation for {}".format(updated_count, user.username))

    user.profile.vacation_date = None
    user.profile.on_vacation = False
    user.profile.save()

UPDATE: If I remove the F() expressions, and replace them with a for loop, this error disappears. Like so:

    for rev in users_reviews:
        lst = rev.last_studied
        nsd = rev.next_review_date
        rev.last_studied = lst + elapsed_vacation_time
        rev.next_review_date = nsd + elapsed_vacation_time
        rev.save()

I noticed in the release notes for 1.9 that they had added a TIME_ZONE attribute for timezone-naive databases (like SQLite, which is what I run my tests with). I've tried adding my timezone to the DB config, but the issue persists. Any ideas? Here are my timezone-related settings in settings.py

MY_TIME_ZONE = 'America/New_York'
TIME_ZONE = MY_TIME_ZONE
DATABASES = {
        'default': {
            'ENGINE': 'django.db.backends.sqlite3',
            'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
            'TIME_ZONE': MY_TIME_ZONE
        }

Answer 1

Eventually after hassling the core developers, I found that this is indeed a bug, specifically when using SQLite. It is documented here, but is still unfixed:

https://code.djangoproject.com/ticket/27544