When playing a disk in a Jukebox, it will power an activator rail directly below it, but a hopper minecart on that rail still sucks the music disk out before it has chance to play.
1) Place a Jukebox 1 block up in the air
2) Place an activator rail directly below the Jukebox
3) Place a hopper minecart on the activator rail (rail should be un-powered at this point)
4) Put a disk in the Jukebox
5) Watch the jukebox briefly power the activator rail
6) The disk is sucked out of the Jukebox by the hopper minecart sat on the powered activator rail
When the Jukebox plays a disk, the Jukebox should power the activator rail and prevent the hopper minecart from sucking the disk out until the Jukebox turns off (either by the disk ending, or the disk being ejected), any ejected disks landing on top of the Jukebox should then be collected by the hopper minecart as the activator rail would then be turned off.
This issue was highlighted due to a recent parity update, to match Java, that allows a hopper minecart to suck disks out of a Jukebox when it goes under it.