The Bug:

Edit: Initially, I thought this bug was about if you reload a world after a Jukebox has finished playing music but left the disc in, it would still let you dupe Allays. However, after the addition of the Jukebox particle and more testing, I was able to figure out I was wrong; this is what actually happens. I was thinking the Jukebox song was over because the audio had stopped, but it was still technically going as the audio and "playtime" of the jukebox aren't actually synced.

If you relog a Minecraft world while a Jukebox is playing, the Jukebox will continue to act like it is playing music; producing a particle and letting you dupe Allays. However no audio will be heard.

How to Reproduce:

1. Play a disc on a Jukebox, preferably with an Allay nearby.
2. Wait until the music track ends, then reload the world
3. Once logged back in, notice how the jukeblox with continue playing notes, emitting redstone, and allowing Allays to be duplicated despite no longer playing audio