QSharedPointer won't take ownership of a QObject that has once had a parent if QT3_SUPPORT is defined

When building Qt 4.8.0 with QT3_SUPPORT and QT_SHAREDPOINTER_TRACK_POINTERS, the following program crashes.

QWidget w1;
QWidget *w2 = new QWidget(&w1);
w2->setParent(nullptr);
QSharedPointer<QWidget> sp(w2); // crash: QSharedPointer: pointer %p already has reference counting

It looks like it is due to the QT3_SUPPORT-specific code in QObjectPrivate::setParent_helper(QObject *)