Not sure this is a bug, but it is definately a useability issue. If you create a playlist, say "Pearl Jam" and add the album "Ten", then create another playlist, "Music I like", and copy "Ten" into it, if you delete tracks from "Ten" in the "Music I LIke" playlist, they will also be deleted from the original "Pearl Jam->Ten" playlist.

Shouldn't the playlists be separate?!

EDIT ... Oh yeah...this is with Beta13