MDI Sub window title remains in main window title when DontMaximizeSubWindowOnActivation option used

In the sample of <QtInstallation>\Examples\Qt-5.15.3\widgets\mainwindows\mdi\
Added mdiArea->setOption(QMdiArea::DontMaximizeSubWindowOnActivation); in MainWindow::MainWindow() function. 

To reproduce:

Create 1st sub window, maximize it, create 2rd sub window, maximize it, the title of 1st sub window will remain in the main window title bar no matter what operation being done from here