Headphone jack port stopped working after opening Audacity

I found a workaround that I described in the bug report mentioned in the other answer (bug 1257956, related to bug 1018262).

I went into Audacity and changed the microphone source in the drop-down menu from "sysdefault: Headphone Mic:0" to "sysdefault: Internal Mic:0" and it fixed it. I can now use my headphones, even when I restart Audacity.

It is apparently a bug with Audacity 2.0.3 to 2.0.5, it messes up Alsa, as described on Launchpad. I haven't found any way to repair this, except reinstalling and not using Audacity.

According to some Google searches, you could maybe bypass that bug using OSS instead of Pulseaudio, or try an older version of Audacity, but I haven't tried it, I'm tired of reinstalling Ubuntu (once with 2.0.3 and once with 2.0.5)