Steps to reproduce:
1) Open and configure any example project with 2 cpp files
2) Open a cpp file from the project, open the second one
3) Use Alt-Tab hotkey a couple of times to switch between the files (this makes the popup appear)
4) Open the Debug -> Start Debugging -> Load Core File menu item (Preferences should work too)
5) Observe that the file switching popup reappears and doesn't go away even if you alt-tab to another application.

Reproducable on two different macOS machines, but not a Windows machine.

Most likely it's a Qt 5.13.1 bug?