Coming from iTunes, I found this to be the most confusing aspect of the app. Everything's a playlist. Sometimes I just want to play an album without making it a playlist. Problem is, double-clicking anything essentially creates a playlist so, as @meow notes, it will overwrite or add to whatever's in the current list. I've wiped out a number of playlists that way before I figured it out.
I would love it if the tabs were actually separate and independent views based on the active tab: a "collection view" a "playlist view" and a "smart playlist view"—and the views don't affect each other.
If you're in the Collection view:
Double clicking displays the song/album/artist in the view window and they become just songs that are playing.
Default sort for artist is albums in ascending chronological order
Songs within albums sort sequentially by disc
Selecting any other song/album/arist doesn't affect anything in the playlist views
If you're in the playlist view (standard):
Double clicking a playlist opens it in the "playlist view" and plays it.
Appending or replacing songs to a playlist should be a deliberate act; replacing should prompt "are you sure?"
Playlists auto-save so there's no need to star anything since it's assumed that creating a playlists means you want it saved.
There would be a way to access the collection while in the playlist view to create the playlists.
If you're in the smart playlist view:
Double clicking a smart playlist opens it in the "playlist view" and plays it.
The edit criteria dialog is accessible and requires a manual save with a prompt if you close without saving (unlike current which doesn't prompt).
