reparenting a QWindow via [win32] SetParent does not work

in my project, I have the following setup:

I create a QOpenGLWindow, which at some point, I have to re-parent to some native WIN32 window. After doing that, my QOpenGL window does not receive any paintGL() calls anymore (it seems its exposed flag is set to false).

I created a minimal repro (attached), which does the following:

it's a standard Qt application, which creates and opens a simple (toplevel) QOpenGL window. When pressing the "Re-Parent" button, it will create a simple QWindow, to which the existing QOpenGLWindow should be re-parented. When trying to do this with native win32 SetParent() - which is what I have to do in the end - all paintGL() calls are gone. When trying it with QWindow::setParent(), the app will crash straight away.

This seems to be Windows only - a similar approach on MacOS works.