QSharedPointer works incorrectly

I have found interesting issue. I attached file to description.
This code crashes. In object B i have destructor:

~B()
{
	QSharedPointer<IB> b = m_a->getB();
}

When i destroy object B, reference to object becames 0. In B destructor reference became 1 and when we leave destructor reference became 0 and QSharedPointer make attempt to delete object again.
Note: boost::shared_pointer solves this situation correctly.