This is very annoying, especially since I work in an office and constantly use my phone as my mp3 player and wear headphones.
When my headphones are plugged in and I receive an email or text message or ANY audible alert on my phone the sound almost always goes from the headphones to the phone speaker. So I hear the alert in my headphones (or through my car stereo when I'm using an FM transmitter or AUX jack) then once the alert sound is over the music stops coming through my headphones and goes through the phone speaker. I have had two different Galaxy S3's and experienced this issue on both very consistently. Not sure it's a Jellybean issue or hardware issue.
When my headphones are plugged in and I receive an email or text message or ANY audible alert on my phone the sound almost always goes from the headphones to the phone speaker. So I hear the alert in my headphones (or through my car stereo when I'm using an FM transmitter or AUX jack) then once the alert sound is over the music stops coming through my headphones and goes through the phone speaker. I have had two different Galaxy S3's and experienced this issue on both very consistently. Not sure it's a Jellybean issue or hardware issue.