QOpenGLWidget is not repainted when repaint is called on parent widget.

I have a custom widget that has a QOpenGLWidget as a child. At some point, I want to update the widget, so I call repaint() on it, expecting that all child widgets, including the QOpenGLWidget get updated as well. But that does not appear to be the case. The attached code reproduces the issue. When the user pushes the button, a timer starts, which calls the onTimer slot. This calls repaint on the parent widget. The QOpenGLWidget child widget, however, does not get updated. Is this by design or is this a bug?