MacOS: QOpenGLWindow::frameSwapped() flood when window is obscured

MacOS only bug:

I have a QOpenGLWindow, where I hooked up frameSwapped() to update() (that's what the documentation suggests). As long as the window is visible, the frameSwapped signal arrives as intended with 60Hz. As soon as the window is fully obscured, however, frameSwapped() will appear with maximum rate (about every 0.2 ms). Triggering update() at this rate results in a huge CPU drain, due to constant flushing of the OpenGL context. Unfortunately, isExposed() does not work, so I cannot determine if my window is actually exposed or not and take precautions accordingly.

See attached repro project.