QOpenGLWindow is rendered on top of QToolBar when the toolbar is expanded

QOpenglWindow is rendered on top of QToolBar when the toolbar is expanded.

We have QMainWindow. There are QToolBar and QOpenGLWindow inside QMainWindow. Toolbar has several actions. Toolbar is too small to contain all actions. Clicking extension should expand toolbar. But after toolbar expanded QOpenGLWindow is rendered on top of QToolBar. See attached screenshots (with normal and expanded toolbar).

Example application source code is attached.