XCB_MAPPING_NOTIFY not delivered when -no-xkb with -xcb-xlib is used

INIT:

Add debug statement in the qxcbconnection.cpp:

        case XCB_MAPPING_NOTIFY:
            qDebug() << "XCB_MAPPING_NOTIFY";
            m_keyboard->handleMappingNotifyEvent((xcb_mapping_notify_event_t *)event);
            break;

1) Compile and run the provided example.
2) Add or remove any keyboard layout from system's keyboard layout settings.

EXPECTED:

Message XCB_MAPPING_NOTIFY in the output.

ACTUAL:

No XCB_MAPPING_NOTIFY message in the output.

class MainWindow : public QWidget
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
protected:

};

MainWindow::MainWindow(QWidget *parent) :
    QWidget(parent)
{
    QVBoxLayout *layout = new QVBoxLayout(this);

    QPushButton *fiveButton = new QPushButton("5");

    QTextEdit *edit = new QTextEdit;

    layout->addWidget(fiveButton);
    layout->addWidget(edit);

    fiveButton->setShortcut(QKeySequence(Qt::Key_5));
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    MainWindow w;
    w.show();

    return a.exec();
}

If we type something in the text field and then repeat the test case, then message XCB_MAPPING_NOTIFY appears in the output - as expected. So unless user triggers QXcbKeyboard::handleKeyEvent (which in turn calls XLookupString) Qt is not receiving mapping notify events which are stuck somewhere in the Xlib's event queue. Related bug report on freedesktop bug tracker https://bugs.freedesktop.org/show_bug.cgi?id=23202

Running test application under:

xtrace ./testapp | grep -i mapping

I can see that MappingNotify is deliver for both test cases, but for some reason Xlib holds it to itself..