title: update() or repaint() fails to trigger paintEvent()
body: <p>I have a QScrollArea fathering my awesome scrolling widget. I like to do updates on the contents on various occasions.</p>
  
  <p>For this I did an override of <code>paintEvent(QPaintEvent *)</code>. Then everytime I want it to be done I call <code>update()</code> on the widget.</p>
  
  <p><strong>Problem:</strong> <code>paintEvent()</code> is never called by this!</p>
  
  <p>What I tried in troubleshooting so far:</p>
  
  <ul>
  <li>Use <code>repaint()</code> instead of <code>update()</code>. Should call it instantanously. Unfortunately does not.</li>
  <li>Test for <code>isVisible()</code> and <code>updatesEnabled</code></li>
  <li>Test wether my override is correct. <strong>Resizing the window calls my function.</strong> Only my manual update(), repaint() calls fail.</li>
  <li>Implement a QTimer to trigger update() or repaint() every 500ms. The trigger gives text output, the function is not called.</li>
  </ul>
  
  <p>Anybody got an idea what to check next? What could make repaint() <em>not</em> call paintEvent()?</p>