Headphone-Speaker Problem

while my headphones are plugged in, the speaker on the back of the phone is still turned on, therefor, music coming out of both ways. wth? please help

Are you saying always be like this?
Are you using Samsung galaxy s gt-i9000?
or only some of applications?
yes... i also having problem with this...

I found is New Yahoo Messenger with voice and video and iMovicha having this issues..
http://www.samsunggalaxysforum.com/samsung-galaxy-s-applications/voice-call-video-call-app/msg6089/#msg6089

What kind application you running having this kind of issue?

I susspect it could be coding of the application doesn't meet requirement to control the application.
it supposed, when hand free cable plug in it will trigger speaker to mute.
Some how it doesn't... weird... not sure application problem or Samsung have different method to do that..
so developer doesn't know about it...

problem solved. the jack was pushed in all the way, that wasn't the problem. thing is, i don't know what was wrong, i turned off the phone and then turned it back on and...it worked. someone asked about the model. it's i9000 galaxy s, i don't know of any "gt" in the name of the phone

I've had a VERY weird issue where sometimes an MP3 being played suddenly has no vocal track.. you unplug the phones and the vocals are there on the loadspeaker..plug the phones back in and it's gone.  Restart the phone and the issue is solved.  VERY WEIRD.