Windows 7 64-bit, GTX 770 OC
Broken: 2.79RC 6af7d7e
Worked: 2.78C e92f235283
Audio tracks will only play once. There appears to be a cache which after an audio segment is cached, it no longer plays.
Playback (alt+A) through an audio clip or Audio Scrub through it and it will play the first time you go over an area; afterwards no sound is played.
Changing Sound settings in Preferences>>System seems to reset this cache, allowing audio to be played once more.