ubuntu 9.10 headphone jack does not work alone, (both speaker and headphone working)

The problem:
I cannot use headphone output only, under ubuntu 9.10
when listening some voice/audio, voice is sent to both headphone and speaker.


install using:

aptitude install gnome-alsamixer

then, run: gnome-alsamixer,

then, click on "headphone jack sense"

thats it..