I was messing around with the new feature of using hoppers to transport the music discs but when it came out, it locked the hopper and prevented music discs from going into the chest. I'm not sure if this was intentional
(image below: Wont go into chest)
The next disc gets pushed into the jukebox before the below hopper can push to the chest, resulting in the jukebox emitting power and locking the hoppers.
Not a bug.