if i put a disc in a jukebox it starts the song and if i take it out, or break the jukebox the song wont stop. if i then close the world it wont stop. if i then reload the same world it will pick off where i 'stopped' it by closing the world, but still play the first one. if i then break the jukebox or take the disc out it will stop the second iteration but wont ever stop the first. so at that point i hear the song twice. if i then close the world i will stop the second song and continue to hear the first until it ends naturally.
if i load another world it stops. but if i load the world where i started the song it will continue, even if i broke the jukebox beforehand. it will also remember where he jukebox was, so if i walk around the song will come from another point in the main menu.
MC-89510 Music Disc continues playing when Jukebox destroyed