By default, PulseAudio allows an application to change the max volume output to be louder than the one set by the user. I find it annoying that some apps tend to set volume to 100% which ends up increasing the system volume to unreasonable levels. You can prevent it by setting
$ echo "flat-volumes = no" >> ~/.config/pulse/daemon.conf $ pulseaudio --kill $ pulseaudio --start
flat-volumes = no PulseAudio uses relative volumes. Each applications sets its own volume relative to the system output.