QMessageBox on mac no longer returns focus to mainwindow that invokes it

Under macOS, the new native QMessageBox upon returning does not return focus/activate the MainWindow that invoked it.

Given the number of QMessageBoxs in an application like Sigil, this bug changes everyone's long standing work flow and gui expectancy by now requiring the focus/activation manually.

See the attached standalone program to recreate the bug.

To run it:

unzip bug_report.zip
cd bug_report
qmake
make

open ./bug_report.app

There is a macos application menubar that differs from the main window menubar. Use the current menubar (Window 1's menubar) menu Test-> Run MessageBox.

Notice the change to the application menubar when the QMessageBox is active.
Click OK

Notice that the application menubar stays, and the MainWindow that invoked the QMessageBox itself is not activated (meaning its menubar is not being shown).

The user now has to click on MainWindow 1 just to get focus back after running the QMessageBox. This bug does not exist in earlier versions of Qt without native QMessageBoxes.

Please fix this.