title: Qt. QDateTime unpredictable behaviour with timezones and addSecs
body: <p>I can't realize what's wrong. </p>
  
  <pre><code>QTimeZone zone1(QTimeZone("Europe/Moscow"));
  QTimeZone zone2(QTimeZone("Asia/Yekaterinburg"));
  QDateTime test = QDateTime(QDate(2016, 11, 11), QTime(15,00), zone1);
  qDebug() &lt;&lt; test;//QDateTime(2016-11-11 15:00:00.000 MSK Qt::TimeSpec(TimeZone) Europe/Moscow)
  test = test.addSecs(5*60);
  qDebug() &lt;&lt; test;//QDateTime(2016-11-11 15:05:00.000 MSK Qt::TimeSpec(TimeZone) Europe/Moscow)
  </code></pre>
  
  <p>This is working fine with Europe/Moscow(+3), but when I change timezone to Asia/Yekaterinburg(+5) it works very strange</p>
  
  <pre><code>QTimeZone zone2(QTimeZone("Asia/Yekaterinburg"));
  QDateTime test = QDateTime(QDate(2016, 11, 11), QTime(15,00), zone2);
  qDebug() &lt;&lt; test;//QDateTime(2016-11-11 15:00:00.000  Qt::TimeSpec(TimeZone) Asia/Yekaterinburg)
  test = test.addSecs(5*60);
  qDebug() &lt;&lt; test;//QDateTime(2016-11-11 10:05:00.000  Qt::TimeSpec(TimeZone) Asia/Yekaterinburg)
  </code></pre>