A separate Window seems to interfere with main Window management on macOS

Reproducer attached. It's confirmed to be a problem on macOS and not a problem on Windows.

Steps to reproduce:
1. Build and run the reproducer
2. Click the button and it's going to show a separate Windows in 2 seconds
3. Minimize the main window within 2 seconds, i.e. before the sub window becomes visible

Expected:
After 2 seconds you can still restore the application and you should be able to see and play with 2 windows

Actual:
Main window cannot be restored anymore and only the sub Window is in foreground. The only way I see right now is to right click on the application icon and "Show All Windows".