title: Django ORM: how count in annotation differ from count on query set?
body: <pre class="lang-py prettyprint-override"><code>qs = ...
  
  qs = qs.annotate(v=Count('a', filter=Q(a__lt=5)))
  a = qs.first().v
  b = qs.filter(Q(a__lt=5)).count()
  
  assert a == b  # error
  </code></pre>
  
  <p>Is there any reason why these methods could produce different results?</p>