When using Ubuntu 15.10, my headphones were auto-detected properly. Since upgrading to 16.04, that is no longer the case. I can force output to them using either pavucontrol or indicator-sound-switcher, and doing so while running pulseaudio in debug mode shows that analog-output-headphones works (obviously).
However, pavucontrol and hdajacksensetest show that headphones being plugged in are no longer detected.
What has changed in 16.04? The sound card in question uses the Realtek ALC3235 codec, using the snd-hda-intel module, from what I can tell.
Some info from dmesg as well:
snd_hda_codec_realtek hdaudioC1D0: autoconfig for ALC3235: line_outs=1 (0x16/0x0/0x0/0x0/0x0) type:line
[ 2.501826] snd_hda_codec_realtek hdaudioC1D0: speaker_outs=1 (0x14/0x0/0x0/0x0/0x0)
[ 2.501829] snd_hda_codec_realtek hdaudioC1D0: hp_outs=1 (0x15/0x0/0x0/0x0/0x0)
[ 2.501831] snd_hda_codec_realtek hdaudioC1D0: mono: mono_out=0x0
[ 2.501832] snd_hda_codec_realtek hdaudioC1D0: inputs:
[ 2.501835] snd_hda_codec_realtek hdaudioC1D0: Dock Mic=0x19
[ 2.501837] snd_hda_codec_realtek hdaudioC1D0: Headset Mic=0x1a
[ 2.501839] snd_hda_codec_realtek hdaudioC1D0: Internal Mic=0x13
[ 2.511782] input: HDA Intel PCH Dock Mic as /devices/pci0000:00/0000:00:1b.0/sound/card1/input10
[ 2.511845] input: HDA Intel PCH Dock Line Out as /devices/pci0000:00/0000:00:1b.0/sound/card1/input11
[ 2.511901] input: HDA Intel PCH Front Headphone as /devices/pci0000:00/0000:00:1b.0/sound/card1/input12
ALSA details: http://www.alsa-project.org/db/?f=b75391807be48e7403a2fd316c18485e15cecb2b