Is there anything else in the pack besides the title?
That is probably because the texture for the music box is on a sheet with many other music boxes. When this update was released, the newer content did not yet exist. The next update should fix this.I'm using the texture pack Terrafine and it seems to have a conflict with the music box "Journey's end", bought from the Princess, because when I use it, the music box is invisible. I've tried using only Terrafine, to see if it was anything else, but it only dissapears with Terrafine, Afram doesn't seem to have any conflict with the new items, as far as I've seen.
It's something that would unfortunately pop up on most 'new content' updates. Some 1.4 textures were spilt into a new texture file but alot of decor items end up stacked into 1 texture file. However with 1.4.1 being labeled as the last update (minus potential bug fixes as '1.4.1.X') there shouldn't be any issues like this coming back around unless the dev team decides to add more content later on.
Depends on how you go about it. I started messing with textures again myself recently and am doing them in my own style trying to keep to the original for most, but improving as i see fit. (Completely remade the king slime trophy's sword for example)HD terraria feels cursed.