Comment 73 for bug 994685

@Herton, as you can see (and modify) in /usr/share/pulseaudio/alsa-mixer/paths/analog-output-headphones.conf, PulseAudio sets "Speaker" to off when the headphones path is activated, which it automatically is, based on the jack detection.

I think the only sane solution here is to create a bugfix patch based on the 3.2 code, something that's smaller than applying the entire "ALSA: hda/realtek - Finer tuning of auto-parser" commit.
This can be done either by using separate DACs for speaker and headphones, or by renaming "Speaker" to "Master", whichever is simplest.