Some MPD Commands don't work 0.979

Hello Volumio Users,

i am working with volumio since Version 1.55 on my Raspberry Pi 2 with Hifiberry Amp+ and i control it
via MPD command like this: -2 2

On Version 1.55 i have changed in mpd.conf as follow:
mixer_control “Master” and also volume works.

But now on Version 0.979, which is really great, i can’t control the Volume via those commands.

Its possible to start stop if i connect with ssh and send the commands via Terminal like this:
mpc start or mpc stop, but also volume control is not possible, which is very important for me.

Thanks for your Help.