/playsound not playing sounds

Both on my server (Ubuntu 14.04) and on singleplayer maps (Ubuntu 15.04), the `/playsound` command is not playing any sound.

All sounds DO play normally when triggered by game events (such as mobs, lava popping, thunder, etc.). All volume is turned up. However, playing any sound via `/playsound`, while claiming success, plays nothing. I have a number of command blocks that used to play sounds, but as of 15w44a, they no longer work.

For example, running "/playsound mob.zombie.hurt @p" should play the Zombie hurt sound to me, but there is no sound. If I hit an actual zombie, however, I hear the sound that relates to that event.

This is the same with captions on and off.

The other person on the server (who is running Windows 8) has confirmed the same problem.