Frameless child-widgets only drawn inside parent/main widget

[ChrillesNet]

I want to be able to have a parent for my child-widget as the default (qt)-behavior. It works as expected if I don't use the frameless widget but when I use the FramelessWindow, the child-window is only visible in front of the parent.

Here'a an example of what I mean:

// Undefine this to switch to windows frame mode
#define FRAMELESS_CHILD

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

    // style our application with custom dark style
    a.setStyle(new DarkStyle);

    // create frameless window (and set windowState or title)
    FramelessWindow framelessWindow;
    framelessWindow.setWindowTitle("Main Window");
    framelessWindow.setWindowIcon(a.style()->standardIcon(QStyle::SP_DesktopIcon));

    // create our mainwindow instance
    MainWindow *mainWindow = new MainWindow;

    // add the mainwindow to our custom frameless window
    framelessWindow.setContent(mainWindow);
    framelessWindow.show();

#ifdef FRAMELESS_CHILD
    FramelessWindow childFramelessWindow(&framelessWindow); // Small difference if mainWindow or framelessWindow is parent.
    childFramelessWindow.setWindowTitle("Child Window");
    framelessWindow.setContent(new QDialog);
    childFramelessWindow.show();
#else
       // Works as expected but with windows/OS frame
    QDialog* child = new QDialog(&framelessWindow);
    child->resize(200, 200);
    child->show();
#endif // FRAMELESS

    return a.exec();
}