title: UIRefreshControl stops spinning after making application inactive
body: <p>I use UIRefreshControl in a UITableView:</p>
  
  <pre><code>UIRefreshControl *refreshControl = [[UIRefreshControl alloc] init];
  [refreshControl addTarget:self action:@selector(refresh)
           forControlEvents:UIControlEventValueChanged]; 
  self.refreshControl = refreshControl;
  </code></pre>
  
  <p>With refresh handler:</p>
  
  <pre><code>-(void)refresh {
      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
          // (...some long running operation...)
          dispatch_async(dispatch_get_main_queue(), ^{
              [self.refreshControl endRefreshing];
          });
      });
  }
  </code></pre>
  
  <p>During the long running operation I make the application inactive pressing Home button. After that I make the application active again. The spinner freezes (stops spinning) and there is no way to return it to the initial state.</p>
  
  <p>How to fix it?</p>