THis chipset (I believe) is controlled at the software (driver) level for the hadphone/speaker switch, it is not a hardware circuit that acts as the switch. I have noticed MANY complaining of this very issue, and the bug is not limited to a specific OS.
out of curiosity is this an alsa mixer or a hardware issue cause as far as i know when you plug in headphones the physical connection for sound to the speakers is disconnected physically . the question is do you have any other operating systems on your pc do the headphones work there . i have mandriva 2008 and 2009 there is no option for headphone sound but when i plug in headphones speaker sound is automatically disconnected