QTabBar / QMdiArea Mac::TabbedView: Paging control is missing

When using a QTabBar / QMdiArea Mac::TabbedView and adding more tabs then can be shown under windows a paging control is added:

on the Mac, this wont appear:

Easy to reproduce - I just added the following lines in MainWindow::MainWindow() of the mdi sample

mdiArea->setViewMode(QMdiArea::TabbedView);
mdiArea->setTabsClosable(true);
mdiArea->setTabsMovable(true);
mdiArea->setDocumentMode(true);