After setting two menus as system at once, you won't be able to set first menu as system again.
Reproducible: Always
Platform-specific: yes, macos only
Is a regression: no
Steps to reproduce: run attached sample.
1. Click "A as system", you will see A menu bar as macos system menu.
2. Click "B as system", you will see B menu bar as macos system menu.
Expected result: Pressing buttons again will set related menu as system
Actual result: You can't set A menu as system anymore, but B could be set.