SUMMARY STEPS TO REPRODUCE 1. Choose "Add virtual output device for simultaneous output on all local sound cards" in System Settings / Multimedia / Audio Volume / Advanced. 2. Set the virtual output device "Simultaneous output to XXX, YYY" the default. 3. Plug in audio device ZZZ. OBSERVED RESULT The name for the simultaneous output has a new name: "Simultaneous output to XXX, YYY, ZZZ". Now, *the default audio device has automatically changed to ZZZ.* EXPECTED RESULT The simultaneous output should remain the default device regardless of the hardware output devices plugged into the system. SOFTWARE/OS VERSIONS Linux: kernel 5.0.0-29 on Kubuntu 19.04 KDE Plasma Version: 5.16.5 KDE Frameworks Version: 5.62.0 Qt Version: 5.12.2 ADDITIONAL INFORMATION It would be useful to have the default stay the same (if it is the simultaneous output): this way one can consistently set the volume of all the outputs together using the main volume control, or for example quickly mute everything -- even after something is plugged in or out.
*** Bug 436239 has been marked as a duplicate of this bug. ***
I can reproduce the behavior, but only with "Automatically switch all running streams when a new output becomes available". Technically it makes sense since, well, a new output is available. I don't disagree that the combined output should be special here. However the behavior is purely up to PulseAudio and Plasma has no influence over it. Can you please report this to https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues ?
Thanks for your interest and the link. I have now reported the bug upstream. https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues/1273