opening a context menu over a QGLWidget causes a warning in setTransientParent

In qtbase/examples/opengl/legacy/hellogl it can be reproduced like this:

void GLWidget::mousePressEvent(QMouseEvent *event)
{
    lastPos = event->pos();
    if (event->button() == Qt::RightButton) {
        QMenu m(this);
        m.addAction("test item");
        m.exec(event->globalPos());
    }
}

You will get a warning like

void QWindow::setTransientParent(QWindow *) QWidgetWindow(0x118c39a10, name = "QWidgetClassWindow") must be a top level window

with a stack trace something like this

0	QWindow::setTransientParent(QWindow*)	qwindow.cpp	1131	0x10969ac1a	
1	QWidgetPrivate::setParent_sys(QWidget*, QFlags<Qt::WindowType>)	qwidget.cpp	10516	0x10898b528	
2	QWidget::setParent(QWidget*, QFlags<Qt::WindowType>)	qwidget.cpp	10375	0x108971b07	
3	QWidgetPrivate::init(QWidget*, QFlags<Qt::WindowType>)	qwidget.cpp	1179	0x10896fe3c	
4	QWidget	qwidget.cpp	1026	0x1089701a9	
5	QMenu	qmenu.cpp	1333	0x108b3468f	

I see a couple of problems:

1) if a widget tries to set its transient parent to a non-top-level window, why don't we go up the hierarchy to find the top-level one? (The reason that it's not top-level is that QGLWidget renders into a window which is an inner child of the parent widget's window.)

2) why is QMenu doing that? It has to control its own absolute position anyway, so the transient relationship is probably irrelevant.