title: A change in eventFilter function causes weird QGraphicScene behavior
body: <p>I have a Qt program with a QGraphicScene inside a QGraphicsView on top of QMainWindow.
  The events are handled by the QMainWindow using an eventFilter function.
  The function body looks similar to this code:</p>
  
  <pre><code>bool Window::eventFilter(QObject *, QEvent *event) {
    QEvent::Type type = event-&gt;type();
  
    if (type == QEvent::KeyPress) {
      QKeyEvent *keyEvent = static_cast&lt;QKeyEvent *&gt;(event);
  
      switch(keyEvent-&gt;key()) {
      case Qt::Key_A:
      case Qt::Key_B:
      case Qt::Key_C:
      case Qt::Key_D:
        // call a function that uses the current mouse position on the graphics scene
        break;
      default:
        QLocale loc = QApplication::keyboardInputLocale();
        if(loc.language() != QLocale::English) {
          QString message = "A non-English key was pressed";
          showMessage(message, QMessageBox::Warning);
        }
      }
  
      return true;
    }
  
    return false;
  }
  </code></pre>
  
  <p>I recently added the "default" part and since then the coordinates that are used in the A,B,C,D cases are totally wrong. In addition, if I add a simple cout print anywhere in the function the bug disappears and the correct mouse coordinates are used.</p>
  
  <p>What can possibly cause this?</p>