Comment 4 for bug 769274

It doesn't appear that saving the settings changes anything in ~/.kde/share/config/phonondevices. When I save a different ordering of devices, the datestamp on the file doesn't change, and the only file whose datestamp changes is ~/.kde/share/config/systemsettingsrc which has no information about sound devices.

There are also two files in ~/.config/kde.org/, but neither of them are relevant as well. I've looked in a couple of other likely spots and cannot find any configuration file that is changed when I save settings in this dialog.

As the poster of https://bugs.launchpad.net/ubuntu/+source/phonon/+bug/638965, I can confirm that it has nothing to do with that report. (In fact, I later determined that I had missed the prefer/defer buttons.)