Comment 4 for bug 1464321

http://cgit.freedesktop.org/pulseaudio/pulseaudio/commit/src/modules/alsa/mixer/paths/analog-output-headphones.conf?id=594da41d07edcebc5fd319388852a66cc3f12ace

http://cgit.freedesktop.org/pulseaudio/pulseaudio/tree/src/modules/alsa/mixer/paths/analog-output-lineout.conf

if it is dock line out, look like you need to add

[Jack Dock Line Out]
required-any = any

otherwise you need to use hdajackretask to change dock line out to dock headphone

http://voices.canonical.com/david.henningsson/2011/11/29/turn-your-mic-jack-into-a-headphone-jack/