Stop all other sounds when activated not working

[Nollidw]

As you can see from the title, the "Stop all other sounds when activated" button is not working as intended. I was trying to assign it to a midi to stop all the other sounds when I press it but, the sounds just overlap on top of each other. I tried restarting the program, deactivating it then activating it, different midi, and nothing seems to work.

Is there anything I am doing wrong or does anyone know a fix to this problem?