title: Django (v1.11.3) UnorderedObjectListWarning even though list is ordered
body: <p>I keep running into Django's <code>UnorderedObjectListWarning</code> when trying to display model instances in a paginated view for search results. However, there is a default ordering defined in the models.py file: </p>
  
  <pre><code>class Rfc(models.Model):
      class Meta:
          verbose_name='RFC'
          verbose_name_plural='RFCs'
          ordering=['number']
  </code></pre>
  
  <p>The actual search happens in views.py and is defined as follows:</p>
  
  <pre><code># parse GET parameters
  search_term = request.GET.get('q', '')
  category = request.GET.get('c', 'cs')
  page = request.GET.get('p', 1)
  
  ...
  
  results_rfc = Rfc.objects.filter(
      Q(title__icontains=search_term) | Q(number__icontains=search_term)
  )
  
  if category=='cs':
      active_tab = 'cs'
      results = results_cs
  else:
      active_tab = 'rfc'
      results = results_rfc
  
  paginator = Paginator(results, 15)
  </code></pre>
  
  <p>However, I cannot seem to make it work, even when explicitly telling Django to <code>order_by('number')</code> in the filter function above. The result is always: </p>
  
  <pre><code>UnorderedObjectListWarning: Pagination may yield inconsistent results with an unordered object_list: &lt;class 'directory.models.Rfc'&gt; QuerySet.
  paginator = Paginator(results, 15)
  </code></pre>
  
  <p>What baffles me even more is that this warning is not displayed when executing above code in <code>manage.py shell</code>. Clearly, I am missing something here. Any ideas?</p>