QShortcutMap::dispatchEvent simply returns, if only disabled matches are found for the current key sequence. It would be helpful to get a signal or event at this point in order to implement a minimal response for the user, e.g. a QApplication::beep().

void QShortcutMap::dispatchEvent(QKeyEvent *e)
{
    Q_D(QShortcutMap);
    if (!d->identicals.size())
        return; // <== emit signal or event here (emit qApp->...)