Comment 11 for bug 1442428

If I understood your question right, that's exactly what happens:

1) I disconnected my speakers from the rear jack, and plugged my headphones into the front jack. After rebooting, the headphones are detected and the sound works - everything is perfect. I opened the Sound Settings dialog, and "Headphones" are present, "Line Out" is absent.

2) I plugged my speakers into the rear jack, and sound immediately stopped playing from the headphones. But the speakers are also silent, even though they're not muted in the GUI. I try muting and unmuting, switching between headphones and line out in the GUI, but nothing works - neither the speakers, nor the headphones.

3) I unplug the headphones, and the speakers start to work. I plug the headphones back in and they start to work, and the speakers are muted (even if I manually select line out from the GUI).

Now, both my headphones and speakers are plugged in, and I decide to test the original bug again:

4) I reboot my system: No Ubuntu welcome sound (the drum sound when the lightdm greeter appears) is played. But when I log in and get to the desktop, the headphones work. The sound settings GUI shows both headphones and line out, and headphones are selected.

5) I suspend and resume the PC. The headphones stop working, and they are gone from the sound settings GUI.

6) I reboot again: Now, the Ubuntu welcome sound plays from the speakers. Headphones are silent. I log in and check the sound settings GUI: line out is present, headphones are absent. Unplugging and plugging in the headphones makes them detected and selected by default in the GUI, and the headphones start working.

So, to correct my original description: Suspend/shutdown has a different effect from rebooting the system.