QMainWindow::GroupedDragging produces wrong title bar

Open examples\widgets\mainwindows\dockwidgets

In MainWindow::createDockWindows()

add: setDockOptions(QMainWindow::AllowNestedDocks | QMainWindow::AllowTabbedDocks | QMainWindow::GroupedDragging | QMainWindow::AnimatedDocks);

• Make the 'customers' and 'paragraph' floating docks
• Drag 'customers' into 'paragraph'
  You now have a floating group, with two tabs
• Double click the title
  Now they are separated, but have the same title.

See attached animated .gif