title: Can't add minimize button to QDialog under linux
body: <p>I'm trying to add a minimize button to my QDialog using this code in the constructor:</p>
  
  <pre><code>Qt::WindowFlags flags = windowFlags();
  flags |= Qt::WindowMinMaxButtonsHint;
  setWindowFlags(flags);
  </code></pre>
  
  <p>It's working on Windows but not on Linux.</p>