The documentation states that only the destructor and assignment operator can deallocate memory:

Note that the internal array only ever gets bigger over the life of the list. It never shrinks. The internal array is deallocated by the destructor and by the assignment operator, when one list is assigned to another.

However it happens in the clear() function as well, which is implemented using the assignment operator:

template <typename T>
Q_OUTOFLINE_TEMPLATE void QList<T>::clear()
{
    *this = QList<T>();
}

You should either fix the doc, or modify clear() so that it doesn't deallocate memory. The second option would be more convenient, and more consistent with what the standard C++ library does. Currently, the only option for clearing a QList without deallocating memory is to iterate and remove elements one by one until the list is empty, which is probably not as optimal as clear() could be.

If QList::clear() is modified, you should consider modifying QVector::clear() as well.