QOpenGLWidget with NativeWindow QDockWidget does not render when undocked

When a QMainWindow with a WA_NativeWindow QDockWidget containing a QOpenGLWidget is shown, and then undocked from the QMainWindow, the OpenGL content ceases to update it's rendering.

The key here is that this erroneous behavior shows if either the QDockWidget, or the QOpenGLWidget are requested to be created as native windows with the Qt::WA_NativeWindow Widget attribute. This also shows if you set the application attribute Qt::AA_NativeWindows.

QTBUG-85714.7z is a small example I attached that reproduces the issue.

To reproduce:

• Build with Qt Creator versions 5.12.9 or 5.15.0
• Run the app.
• You should see that the OpenGL content renders and is interactive.
• Undock the QDockWidget.
• You should now see that the OpenGL content rendering ceases to update.
• Dock the QDockWidget.
• Rendering updates once again happen.

Does not appear to be reproduceable on macOS (10.15.4 tested, built with Qt 5.15.0)