Hi hiccup, thanks for a swift reply!
I will try to explain why it seems a bug to me.
When you select multiple playlists to send the song to, each of playlists you pick is marked with a check mark. So when you're done picking, you have a list of several items you've picked. And when you have a list, you assume that list to be relevant to one parent item.
But that's not the case, because the first playlist from the list goes to the song A, next one goes to the song B, etc.
Furthermore, if you click on one playlist several times, the check mark remains there, instead of being unchecked on every even click on it and checked again on every odd click.
And one more point here: when an item has a context menu with a set of options, you'd expect that every choice you make in that menu would go to the item you originally summoned that menu for. And if you want to work with another item, you would summon a menu for that another item.
If my understanding is wrong and this still doesn't justify this being a bug, please let me know and we'll consider this topic closed.
Thanks.