pixeltool broken in 5.12 on Mac

The pixeltool.app created by building the QtSDK no longer works correctly on macOS in 5.12.0-beta4. Our Windows build does not have this regression.

We are upgrading from 5.9.6 and this is our first build of 5.12, so we do not know when this regression started.

The corruption of the pixels scaled pixels starts when the mouse is in the top left corner of the main display. Notice that 

and gets progressively more distorted moving the cursor to the right or down.

Curiously, there is a cursor location where the screen area is scaled correctly.

Please note that neither of my monitors if set to support HiDPI mode.

This likely indicates Qt code to grab part of the screen is broken on the Mac as well.