Comment 8 for bug 769274

I did try the workaround suggested by Jukka, but my motherboard comes with a 7.1 sound card and the microphone jack is always that, a microphone jack.

As for my workaround with pavucontrol: the application for which you want to change the input/output device, must be active and playing/recording sound.

In the case of Skype, calling the nice lady from "Skype Test Call" and changing the input device at the same time does the trick.
Once you change it, it is remembered, so you don't have to do it again.

This is not a major bug, but it can be a real show-stopper especially for newcomers.