I remember having similar problem with kde4 knotify https://bugs.kde.org/show_bug.cgi?id=324975 and https://bugs.kde.org/show_bug.cgi?id=345651. I can still partly reproduce this with KF5 and gstreamer backend by playing notification and adjusting the notification volume to 100%. After this the master volume is raised to 100% but all the other streams are lowered to keep the same voume level.
Since this is probably a very complicated issue that might be caused by > pulseaudio, > phonon, vlc as phonon backend or kdelibs, and it will probably take many > years to be > fixed, I suggest to ship plasma with a sane default and disable all audio > notifications by default. > The second upstream bug says that gstreamer backend should manage the volumes better. Could you try that?
