QGraphicsScene always in inactive state if placed in a QTabWidget

1. Create QTabWidget
2. Add two tabs - with QGraphicsView and empty.
3. Hide the QTabWidget, the QGraphicsView will receives QEvent::Hide and send event to a QGraphicsScene:

case QEvent::Hide:
// spontaneous event will generate a WindowDeactivate.
if (!event->spontaneous() && d->scene && isActiveWindow())

{ QEvent windowDeactivate(QEvent::WindowDeactivate); QApplication::sendEvent(d->scene, &windowDeactivate); }

break;

....

case QEvent::WindowDeactivate:
if (!-d>activationRefCount) {

Here activationRefCount will equal to 0.

4. Change current tab from scene to another. QGraphicsView will receives QEvent::Hide again. So activationRefCount will equal to -1.
5. Make QTabWidget visible.
6. Switch to tab with the QGraphicsView - it will receives QEvent::Show event and activationRefCount will equal to 0. But that's wrong - because we have active tab with the scene.

Please see screencast: https://www.youtube.com/watch?v=dU3eG94XUQ8

(sorry for my English).