Parts plays back all instruments

When playing a part (File -> parts) that has less instruments than the main file it will play all instruments, or the main file.

I make practise files for my choirs, mp3, midi and Musescore files. So for me it's essential to easily create different files with a single voice + accompaniment.

The workaround is to use the mixer, export the file with that settings and repeat for all the voices.