Windows/Desktop GL app fails to redraw when Windows 10 screen woken

We are seeing rendering-related issues with our Qt Quick 5.9 app running full-screen on Windows 10.

1. After Windows turns the device's display off to save power, pressing a key to re-wake the device reveals a stale image of the app (or an image of the desktop).  The image is frozen, it seems the app is interacting correctly when clicked on, but the image doesn't update.  Pressing the Windows key makes the screen update again.
2. Similarly, pressing the Print Screen key captures old out of date images of the app.
3. Going to and from Task View (smaller representation of running apps, tiled across the desktop) shows similar stale renderings.

These things only happen when running full-screen, if the app is windowed, it's all fine.

I can reproduce this with the Qt Quick Example "Windows and Screen".  I run it and tick Full Screen on the Control Window.  I see a full screen Second Window.  Now I wait for the screen to turn off (I've configured it in Windows to only wait 1 minute).  Wait a few seconds more, then press any key.  The screen turns on again.  But now I'm seeing the Control Window again.  It and everything behind it are frozen, I'm clearly interacting with the Second Window, but that's not being drawn.  If I go to Task View (swipe-in-from-left) a "Control window" thumbnail is shown, along with one called "Test Window with color..." but the latter's thumbnail is not shown.
None of this happens if I instead check Maximized on the Control Window.