I use Google Play music as well and have experienced some issues with music playback too. When streaming from the phone through Bluetooth to my Pioneer DEH-80PRS head unit, I get dropouts in music playback with the error message "Music Playback Error. Couldn't playback the track you requested." If I hit play to restart the song, it fails again almost immediately. I have to change to a new song and back again to try again.
Actually, this happens while I am using my Bluebuds X headphones as well... I haven't used it at length with a wired headphone set or the phone speaker, so I cannot vouch for it being strictly a Bluetooth issue, though I think that is where I would start. I'll grab a Logcat next time it happens - maybe somebody will see something I don't.
Sent from my LG-D800 using Tapatalk