Disabling "flat-volumes" in pulseaudio
Today I've just faced another of those happy ideas some people implements in software, which can be useful for some cases, but can also also be bad as default behaviour.
The problems caused were already posted to Debian mailing lists, fortunately, as well as its solution, which basically in a default Debian configuration means to:
$ sudo echo "flat-volumes = no" >> /etc/pulse/daemon.conf $ pulseaudio -k && pulseaudio
And I think the default for Stretch should be set as above: raising volume to 100% just because of a system notification, while useful for some, it's not what common users expect.