QOpenGLWidget: impossible to grab full QPainter.

Story

I try to grab a custom QOpenGLWidget with OpenGL + QPainter rendering.
I use the Qt Example qopenglwidget with new button to grab all views. See attached program.

Result

When I try to grad widget, just OpenGL part is shown (and recursive grab too for main view).
See attached dump file (where FPS and bubbles are missing).

Expected

Full grab of widget (like printed on screen).

Remark

Moreover, my final aims is to grab parent widget using recursive call of grab(). So if solution is to call another method, my question is: it's recursive too ?