Shoutbox

well, im on my new computer (xmas...) but i still havent figured this out.

on my older computer if i plug a set of headphones or speakers into the headphone jack on the front, the speakers or whatever audio device is plugged into the audio output jack on the back get cut of (as they are ment to AFAIK...)

but on my new one, if you plug headfones in music continues to be output from both jacks...

1 - why?
2 - is there a way to change it?

thanks