ALSA bug? Laptop headphone output depending on speaker channel setting

[Brendon Higgins <brendon@quantumfurball.net>]

Seasonal greetings, Debian users!

I was wondering if anyone has pointers for an audio configuration issue. I have 
Debian Testing running on a Dell laptop (Latitude E6320, audio chipset 
detected as HDA Intel PCH, 92HD90BXX). The speaker output works fine. When I 
plug in headphones, the system seems to detect that okay: it mutes the 
speakers ("Speaker+LO" channel in alsamixer) and unmutes the headphones 
("Headphone" channel).

The problem is that no sound comes out of my headphones.

I've noticed that I have to also unmute and restore volume of the Speaker+LO 
channel to hear anything in the headphones (meanwhile, with headphones 
connected, the laptop speakers are silent as you would expect). The Headphone 
volume setting doesn't seem to matter at all, although muting that does also 
cause the headphones to mute.

It all used to work fine, but probably a couple of years ago it started having 
this behaviour. I suspect it was a kernel update, or maybe ALSA library - I 
can't be certain - and put it off hoping the bug might just get fixed...

Any suggestions? I looked at the hdajackretask app,  but no idea where I would 
even start there.

Thanks in advance,
Brendon