QGraphicsItem crash

void QGraphicsItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
 if (event->button() == Qt::LeftButton && (flags() & ItemIsSelectable)) {
 bool multiSelect = (event->modifiers() & Qt::ControlModifier) != 0;
 if (event->scenePos() == event->buttonDownScenePos(Qt::LeftButton)) {
 // The item didn't move
 if (multiSelect) {
 setSelected(!isSelected());
 } else {
 bool selectionChanged = false;
 if (QGraphicsScene *scene = d_ptr->scene) {
 ++scene->d_func()->selectionChanging;
 // Clear everything but this item. Bypass
 // QGraphicsScene::clearSelection()'s default behavior by
 // temporarily removing this item from the selection list.
 if (d_ptr->selected) {
 scene->d_func()->selectedItems.remove(this);
 foreach (QGraphicsItem *item, scene->d_func()->selectedItems) {
 if (item->isSelected()) {
 selectionChanged = true;
 break;
 }
 }
 }
 scene->clearSelection();
 if (d_ptr->selected)
 scene->d_func()->selectedItems.insert(this);
 --scene->d_func()->selectionChanging;
 if (selectionChanged)
 emit d_ptr->scene->selectionChanged();
 }
 setSelected(true);
 }
 }
 }
 if (d_ptr->scene && !event->buttons())
 d_ptr->scene->d_func()->movingItemsInitialPositions.clear();
}