How to keep a floating dock visible?

[Pieter from Belgium]

I have an application with multiple toplevel windows besides the main window.
I have floating docks.
These docks disappear when I activate a secondary window. They are only shown when the main window has focus.
(How) can I change this behavior, keeping the docks visible whenever any application window has focus?

#include <QMainWindow>
#include <QDockWidget>
#include <QApplication>
 
int main(int argc, char ** argv )
{
    QApplication a( argc, argv );
    QMainWindow* mw = new QMainWindow();
    mw->setWindowTitle("The main window");
 
    QDockWidget* dock = new QDockWidget(mw);
    dock->setFloating(true);
    dock->setWindowTitle("The disappearing dock");
    dock->show();
 
    QWidget* w = new QWidget(mw);
    w->setWindowTitle("The second window");
    w->setWindowFlags(Qt::Window);
    w->setVisible(true);
 
    mw->show();
    return a.exec();
}

#include <QMainWindow>
#include <QDockWidget>
#include <QApplication>

int main(int argc, char ** argv )
{
    QApplication a( argc, argv );
    QMainWindow* mw = new QMainWindow();
    mw->setWindowTitle("The main window");

    QDockWidget* dock = new QDockWidget(mw);
    dock->setFloating(true);
    dock->setWindowTitle("The disappearing dock");
    dock->show();

    QWidget* w = new QWidget(mw);
    w->setWindowTitle("The second window");
    w->setWindowFlags(Qt::Window);
    w->setVisible(true);

    mw->show();
    return a.exec();
}

To copy to clipboard, switch view to plain text mode 

Reproduction:
- place the attached source file in a directory.
- execute qmake -project; qmake;make
- execute the application
- click on "The second window"
Now the dock has disappeared...