I have noticed this happening in the last 2 weeks or so. Every time I create a playlist (or add to an existing playlist) an entire album by highlighting them all, the tracks would get added into the playlist, however the song order would get completely messed up. This is especially frustrating as I prefer to listen to my songs in the order in which they appear in the album. I have had to re-order my songs manually every time I add them into a playlist, which isn't ideal.
If it helps, I'm running OS X 10.10 and my Spotify version is 18.104.22.168.g9977a14b.