I am using Plasma 5, I open the audio control in the tray. If I regulate the sound level by clicking on the regulator and pool it by mouse clicked, than it is OK. But if I scroll the mouse, the audio control regulator moves, but the real sound level does not change. Reproducible: Always
I'm having this bug as well.
This is now fixed: https://quickgit.kde.org/?p=plasma-pa.git&a=commit&h=b75cbce1cbfeb4962f616defde0f0297f28d3147