After setting different volume levels for left and right speaker using pulse audio volume control (PAVU), adjusting the master volume controller in either PAVU or the plasmashell audio volume controller resets both speakers to the same output level. In Gnome and Mate the levels maintain their user-set distinction. There does not seem to be a way in KDE to set the volume levels separately and then adjust the overall volume without having the channels resync undesirably.
*** This bug has been marked as a duplicate of bug 362832 ***