My attention was attracted by the fact that QVector::append
causes the copied object's copy ctor to called twice (unlike when using std::vector)

And indeed, inside:

void QVector<T>::append(const T &t)

the line:

const T copy(t);

seems totally unnessary. I guess:

const T& copy(t);

was the intention.

Anyway, I rebuilt Qt with this small change and my big application is running fine.

Am I missing the obvious?