I've an onboard sound card with a whole lot of profiles (Digital I/O, Analog with lots of channel configurations, etc.). I've set the profile "Analog Duplex" to be the default in the applet and in the Multimedia kcm. If I plug-in a headphone in the front header the output is changed seamlessly to "Headphone"; but when I unplug it the sound profile is reseting to "Digital Stereo Output" instead of "Analog Duplex". I've tried this suggestion [https://wiki.archlinux.org/index.php/PulseAudio#Switch_on_connect] but it doesn't seem to work. openSUSE tumbleweed is affected also.
You should make sure that module-device-manager module is not loaded. Otherwise, the bug is in PulseAudio and you should report it there.
It seems it has been reported (and reopened) there already. Just for the record, here's the upstream bug report: https://bugs.freedesktop.org/show_bug.cgi?id=93903