What's wrong with the music player on my Samsung Galaxy S3?

I just got a Samsung Galaxy S3 a few months ago and am generally in love with the thing. But I listen to audiobooks all the time and have noticed an odd glitch. I usually use Google Play Music because that way I can download files to my phone that are on my computer without paying a lot of money for software. Anyway, when I change the volume of the audiobook while playing a game, the sound stops playing in my earphones and is forced out of the external speakers instead. I have to pull out my earbuds and put them back in, and then press play again on my home screen widget. Why does this happen? Gar.