Comment 8 for bug 921397

Actually a slightly better workaround would be to open
/usr/share/pulseaudio/alsa-mixer/paths/analog-output-headphones.conf

And change:

[Element Speaker]
switch = off

to

[Element Speaker]
switch = mute

...that way the port will switch, which means you can have different volumes for speaker and headphones, but "Speaker playback switch" will not mute when "headphones" is selected.

I have analyzed your issue a bit, but I'm unsure whether this is actually a bug in the codec hardware, or if it's related to the GPIOs. Marking as triaged for now.