QMessageBox before app.exec leads to incorrect focus state

I show a message box before starting the main event loop. After closing the message box, the main application window appears in a bad state:

 - the window does not have focus

 - none of the widgets have focus, and clicking any of the line edits does not make them highlight as expected, yet entering text works.

The application gets to a normal state if I click into a line edit, then switch to a different application and back.

I did not manage to create an example application reproducing all issues in C++. For a complete test application please see PYSIDE-1771. I attached an example application reproducing the window focus issue and screenshots of the behaviour:

 1. Startup: no window focus, line edit has focus highlight, but does not accept input

 2. After clicking on the window titlebar: window has focus, line edit accepts input