Taking out a music disc then quickly placing it back in then taking it out will still play the disc without it in.

This can happen multiple times and play music overlapped with one another.

Destroying the jukebox does not stop the music, it plays as if it was there in  a jukebox.

Only the player who initiated it can hear the music.

Leaving and rejoining or waiting for it to end will stop the music.

This realm is 100% vanilla. I could not replicate this in a singleplayer world.

This link https://youtu.be/eBp4W9IC5Sg shows how to reproduce, and the bug in action.