The current implementatation of QGraphicsScene::clearSelection() has a flaw: QGraphicsItems can override setSelected() with the itemChanged() function. This is not taken into account where the internal state is modified after setSelected( false ) has been called on all items:

foreach (QGraphicsItem *item, d->selectedItems)
    item->setSelected(false);
d->selectedItems.clear(); // <- items may still be selected here

So instead of just clearing the vector, it is required to determine the actually selected items.