Comment 3 for bug 1304074

Well, I've done some research on this

Seems like plugging the headphones in makes pulseaudio change the audio sink port. You can see that by using the

pacmd list | grep "active port"

and when you change active port back to "analog-output-speaker" with headphones connected, everything works fine. Give it a try:

pacmd set-sink-port 0 analog-output-speaker

But I wonder if someone can fix that problem with analog-output-headphones or just automatically change the volume level without changing audio sink port (auto-mute works just fine)