title: NSFetchedResultsController not calling delegate with predicate @count
body: <p>I have a fetched results controller which isn't calling its' delegate when it has a predicate. The predicate is to only include Conversation objects which have <code>events</code>:</p>
  
  <pre><code>    let predicate = NSPredicate(format: "events.@count &gt; 0")
  
      let fetchRequest = Conversation.MR_requestAllSortedBy(
          "mostRecentMessage.eventDate",
          ascending: false,
          withPredicate: predicate)
      self.fetchedResultsController = NSFetchedResultsController(
          fetchRequest: fetchRequest,
          managedObjectContext: MagicalRecordStack.defaultStack()!.context,
          sectionNameKeyPath: nil,
          cacheName: nil)
      self.fetchedResultsController.delegate = self
  
      self.fetchedResultsController.MR_performFetch()
  </code></pre>
  
  <p>This works for an initial fetch, but upon data being added, it doesn't call the delegate. Upon removing the predicate, it does call the delegate.</p>
  
  <p>Is there another way I should be doing this?</p>