I've read many other having this bug, requiring a reset to fix it. Starts to get annoying though. Any word on when a fix us FINALLY coming. Waiting forever for these fixes is ridiculous.
I have the same issue when listening to music or a video and a call comes in which knocks out sound from the right earpiece of my headphones. Once the call is over, I shut down the phone then reboot and back to normal. From what I know this should be taken care of with the official WP8.1 with Cyan update.