I am building the Hello GL example experiment in /qtbase/examples/opengl/hellogl.
I have 2 24" monitors whose native resolution is 1900x1080. If I set the resolution of one monitor to simulate a retina display (960x540 HiDPI) and then build and run the application, when I move the window back and forth between the two monitors, the contents of the QGLWindow often, but not always, display all black or garbage. Moving one of the sliders causes the contents to be repainted correctly.
I would say that the painting gets messed up at least 50% of the time I move the application from one window to another, and it is messed up a bit more often moving from regular DPI to simulated HiDPI than the reverse direction.