pixeltool cannot show pixel grid at correct size on HighDPI screens

The pixeltool that ships with Qt used to be able to show a grid for individual pixels. This has been broken on HighDPI displays for a while since Qt started to introduce more HighDPI support. So when the Windows display scale setting is higher than 100%, the pixel tool no longer displays the pixel grid correctly, even when the grid size is set to the lowest setting.

In Qt 5.9, it is still working as expected. Here, at 150% and 200% scaling, it draws a grid around the actual pixels of my screen:

On recent versions of the pixeltool, the grid can no longer highlight the actual pixels and is a bit too large, even at the lowest setting: