I get this problem more when using HDMI, I think having two digital aduio outputs, outside of default speakers is what causes this type of confusion for my computer (a laptop). Are you playing on a computer hooked up to a TV instead of a monitor, or perhaps a monitor with HDMI or something? Or any other kind of digital audio output that may conflict?

Though I'm kind of speaking out of my ass, since I don't think headphone jacks are even a digital route. But either way, I know this happens a lot when I already have something running and plug in my HDMI. Only things that are opened after the HDMI actually do what they're supposed to. Anything that was previously open usually gets confused and it's random which audio route they choose