title: Django REST Framework: overriding get_queryset() sometimes returns a doubled queryset
body: <p>I made a little endpoint, adapting DRF <code>ReadOnlyModelViewSet</code>, defined as follows:</p>
  
  <pre><code>class MyApi(viewsets.ReadOnlyModelViewSet):
  
      queryset = []
      serializer_class = MySerializer
  
      def get_queryset(self):
          print 'Debug: I am starting...\n\n\n\n'
          # do a lot of things filtering data from Django models by some information on neo4j and saving data in the queryset...
          return self.queryset
  </code></pre>
  
  <p>When I call <code>MyApi</code> via URL, it returns results without any problems, but sometimes it returns doubled result!! It's very strange...It's not a systematic error but happens only sometimes.</p>
  
  <p>I use the line <code>print 'Debug: I am starting...\n\n\n\n'</code> in Apache log to investigate the problem. When that doubling happens, I read in the log:</p>
  
  <pre><code>Debug: I am starting...
  
  
  
  
  Debug: I am starting...
  </code></pre>
  
  <p>It seems like <code>get_queryset</code> is called more than one time. It's very strange. I didn't report the detail of the logic inside that method, I think the problem is elsewhere or that is a bug...How can I solve?</p>