title: Firebase Offline Capabilities and addListenerForSingleValueEvent
body: <p>Whenever I use <code>addListenerForSingleValueEvent</code> with <code>setPersistenceEnabled(true)</code>, I only manage to get a local offline copy of <code>DataSnapshot</code> and <strong>NOT</strong> the updated <code>DataSnapshot</code> from the server.</p>
  
  <p>However, if I use <code>addValueEventListener</code> with <code>setPersistenceEnabled(true)</code>, I can get the latest copy of <code>DataSnapshot</code> from the server.</p>
  
  <p>Is this normal for <code>addListenerForSingleValueEvent</code> as it only searches <code>DataSnapshot</code> locally (offline) and removes its listener after successfully retrieving <code>DataSnapshot</code> <strong>ONCE</strong> (either offline or online)?</p>