no sound on headphone after plugging it in

[Bart de Koning]

After connecting a headphone, the speaker channel is set to zero, which sounds like a logical thing to do, however it dimishes sound on the headphone channel as well. As a workaround I currently start alsamixer from a terminal, switch on the speaker channel (navigate to the speaker channel and hit "m") and increase the volume for this channel. Then still no sound is emitted through the speakers (as you would expect), but it enabled sound from the headphones.
It looks like that the channels are programmed in serial for headphone usage, instead of parallel like the controlling software (and users like me) expect it. In the former versions of Ubuntu this had always worked like a charm, so it appears to be a bug that is introduced recently.

Kind regards, Bart

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: alsa-utils 1.0.28-1ubuntu2
ProcVersionSignature: Ubuntu 3.19.0-16.16-generic 3.19.3
Uname: Linux 3.19.0-16-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed May 20 09:16:36 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-05-12 (7 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: alsa-utils
UpgradeStatus: No upgrade log present (probably fresh install)