title: Swift presentViewController completion block working only in debug not called in release
body: <p>I have a strange behaviour with a completion block in Debug and Release.
  For example:</p>
  
  <pre><code>        sourceViewController.presentViewController(ccVC, animated: true, completion: { () -&gt; Void in
              NSUserDefaults.standardUserDefaults().setBool(true, forKey: kChromeCastInstructionsShown)
              NSUserDefaults.standardUserDefaults().synchronize()
              println("save bolean")
          })
  </code></pre>
  
  <p>In debug:
     println("save bolean") print string
  In relase:
   println("save bolean") print nothing</p>
  
  <p>Any idea about this behaviour?
  Someone experiment a clear solution?</p>
  
  <p>Kind
  Andrea</p>