title: ManyRelatedManager call returns empty list when it should return at least one result
body: <p>I have two models designated for tracking what users have upvoted an Article instance (in another app, in this case <code>articlescraper</code>).</p>
  
  <pre><code>from django.contrib.auth.models import User
  
  class UserProfile(models.Model):
      user = models.OneToOneField(User)
  
      articles_upvoted = models.ManyToManyField('useraccounts.UpvotedArticle',
                                                null=True,
                                                blank=True)
  
  class UpvotedArticle(models.Model):
      article = models.ForeignKey('articlescraper.Article')
      user = models.ForeignKey(User)
  </code></pre>
  
  <p>In a Django shell, I've tried to get a list of articles by interacting with <code>UserProfile</code>:</p>
  
  <pre><code>a = UserProfile.objects.get(pk=1)
  a.articles_upvoted.all()
  </code></pre>
  
  <p>Which returns:</p>
  
  <pre><code>[]
  </code></pre>
  
  <p>However, then I went a little further:</p>
  
  <pre><code>b = UpvotedArticle.objects.filter(user=User.objects.get(pk=1))
  b
  </code></pre>
  
  <p>Which returns:</p>
  
  <pre><code>[&lt;UpvotedArticle: Arch Linux Lexmark S305 Drivers&gt;, &lt;UpvotedArticle: Structure of a Haystack project&gt;]
  </code></pre>
  
  <p>Which is the expected behavior, and is mirrored in the Django admin in both <code>UserProfile</code> and <code>UpvotedArticle</code> categories.</p>
  
  <p>I don't understand, however, why attempting to get a list of articles can't be done the way I initially tried to using <code>a.articles_upvoted.all()</code> if the two models are linked.</p>