Yes and no; MC-98075 doesn't say anything about notes sent with packets that are controlled with the Music slider. However I didn't find this one and should comment on it instead on making another one, so thanks.
Yes, but this is a bug with Minecraft client. It has nothing to do with plugins; I only gave it as a source example. The problem is with not treating noteblock sound properly - as Music and as Block sounds depending on the source - if it's from the Noteblock, it's "Block"; if it's from the packet within the server, it's "Music". If it was a Bukkit/Spigot problem I would report it there.
Also, I think that "Confirmed on Singleplayer" closes that pointless discussion. It is definitely a Minecraft Client bug.
Additionally, when a Note packet is recieved by a client, its volume is set with the "Music" slider.