Speakers don't mute when headphones plugged in?

[Svensander]

basically, i used to plug my headphones into the headphone jack on the speaker remote (logitech LS21 speakers), but for some reason, that was too quiet.
i was surprised that when i plugged them into the 'speaker out' jack on the bass speaker, the sound coming through was SO much louder, and i could actually control the volume using the little volume wheel on the speaker remote - something i couldn't do before...
but when i took the headphones off with the music still playing, i noticed that the sound was simultanously coming from the speakers as well.
how could i fix this?

 

[Svensander]

UPDATE

i don't know how, but after a quick restart, when i plugged my headphones in, no more sound started coming through the speakers anymore!!! and they're so much louder now!! the only problem is the slight static in the background, but at least now my problems are over
HOORAY

 

[Svensander]

UPDATE

i don't know how, but after a quick restart, when i plugged my headphones in, no more sound started coming through the speakers anymore!!! and they're so much louder now!! the only problem is the slight static in the background, but at least now my problems are over
HOORAY