stretch/KDE: system notifications at 100% volume

[solitone <solitone@mail.com>]

Hi,

I'm on stretch, and use KDE plasma desktop. Whenever I get a notification, the 
Built-in Audio Analog Stereo volume jumps to 100%, irrespective of the volume 
level I previously set (e.g. 50%). This means that the notification sound is 
louder than I'd like. Besides, also all other later sounds are too loud. As a 
consequence, I need to lower again the volume manually, but at the next 
notification I have the same issue. If the Built-in Audio Analog Stereo output 
is muted, it stays muted even when notifications occur, but obviously this is 
just a workaound to avoid those loud sounds, not a real solution--I'd rather 
keep volume at 50% or something.

If I go to Audio Volume Settings->Audio Volume->Applications, I notice that 
Notification Sounds are set to 0%, and I cannot change that setting--when I try 
and rise it to whatever value, it goes back to 0%. I don't know whether this 
is somehow realted to my issue, though.

Is anyone experiencing my same issue with KDE on stretch?

Thanks!