QGraphicsScene doesn't enter drag event

[Radagast]

Qt 4.3.2, MS VS 2005+integration
I derived my MyGraphicsScene from QGraphicsScene and reimplemented:

void MyGraphicsScene::dragEnterEvent(QGraphicsSceneDragDropEvent* event)
{
	QApplication::setOverrideCursor(Qt::ClosedHandCursor);
	QGraphicsScene::dragEnterEvent(event);
}
void MyGraphicsScene::dragLeaveEvent(QGraphicsSceneDragDropEvent* event)
{
	QApplication::restoreOverrideCursor();
	QGraphicsScene::dragLeaveEvent(event);  
}

void MyGraphicsScene::dragEnterEvent(QGraphicsSceneDragDropEvent* event)
{
	QApplication::setOverrideCursor(Qt::ClosedHandCursor);
	QGraphicsScene::dragEnterEvent(event);
}
void MyGraphicsScene::dragLeaveEvent(QGraphicsSceneDragDropEvent* event)
{
	QApplication::restoreOverrideCursor();
	QGraphicsScene::dragLeaveEvent(event);  
}

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also my QGraphicsView has DragMode RubberBandDrag enabled.
But while dragging the mouse cursor doesn't changes the dragging itself runs OK.
then I put breakpoints into both functions and realized that the application even doesn't enters them.
I searched this forum and google but didn't find an answer...
Thanks in advance