This is a long standing bug for me and i have only now got around to reporting it. This bug effects most versions of minecraft.
When using two output devices (speakers). If you change the output device minecraft has issues and in the majority of the versions would kill the sound so you couldn't hear minecraft sounds.
However in the latest release version it just stays locked to one output device forcing you to close and reopen minecraft to change audio output devices.
Duplicates MC-19443 (won't fix).