5.10.1 -> 5.11.2 QCocoaScreen->grabWindow is getting the wrong geometry and warping output

In Qt 5.11.2 on Mac (both High Sierra and Mojave), grabWindow seems to completely fail with our setup. Code that has previously worked for screenshotting part of the current window now gives a warped chunk at the wrong offset.

To test this I've used the Qt "Screenshot" example app, and attached screenshots of how it works on 5.10.1 and 5.11.2 on my Mac.

In the 5.10.1 screenshot, there is no warping, and my primary screen is in the correct place on the left hand side. I have a secondary monitor attached which is switched off, hence the blank space on the right.

In the 5.11.2 screenshot, you can see a bit of QtCreator on the right hand side, but it's warped. It should be on the left anyway according to my screen configuration, and for some reason rather than being transparent the "empty" area is blue.

I haven't changed my screen configuration at all between taking the screenshots, and the Screenshot example app is at approximately the same size in both cases, with only Qt Creator visible on screen.

Displays

• iMac, 2560 x 1440 (available 2560 x 1417), 1.0 device pixel ratio
• DELL P2715Q, 1920 x 1080 (available 1920 x 1057), 2.0 device pixel ratio