Command block plays a sound twice if powered by a trapped chest
When powering a commandblock with a trapped chest, /playsound will sometimes play the sound when closing the chest as well as when opening the chest.
It also sounds like when you power it with - for instance - a lever, the sound plays twice simultaneously.
To illustrate, here is a video. I was able to reproduce this several times with the setup I show in the video. (CommandBlock output was disabled).
2014-10-28, 04:43 AM
2015-12-06, 10:11 PM
2015-12-06, 10:11 PM
0
2
-