This just constantly throws up situations where it doesn't behave how I'd expect.
There's a 'Recently Played' smart playlist where I expected to be able to see of all the songs I'd been listening to all day. No, it only shows songs I've recently played that are also in my library. Considering the way Apple Music totally blurs the lines between your library, streaming, radio and purchases, this just seems arbitrary and confusing - a result of jamming Apple Music on top of the iTunes framework I guess.
The back button on the Desktop app doesn't behave properly at all. Hit back and more often than not it takes you back whole sections at a time, not just a single page, leaving it sometimes impossible to get back to the page you were just looking at without jumping through hoops.
Why does the iOS app have the option to download a song for offline straight from the song/album menu but the desktop client doesn't?
The desktop app will let you add a song to library but not remove it from the same menu. If you want to remove it you have to go to My Music.
I'm kinda finding it hard to believe that someone road mapped this interface out and were happy with it. It's just hopelessly confused.