Need help with Pandora, Last.Fm & Slacker

[swissarmy]

When using Pandora, Last.Fm & Slacker using 3G, 4G or Wi-Fi with the screen turned off and locked my music will play as it should. However, as soon as I plug headphones in it will only play one song and then stop. As soon as I turn the screen on and unlock the screen play begins again? I have rebooted and tried this in different locations with the same results. Anybody have any ideas?

Thanks