I recently found out that Spotify creates a playlist with all the songs you have liked from every radio station you listened in the past.
It's really a cool idea of doing that, because I have missed a lot of songs that I liked and now I have them back.
However, the problem with this feature is that it's filled with duplicates, or worse, songs which are there more than 10 times!
I was hopping that this get's fixed, Spotify can tell very well when I have a song in a playlist and if I try to add the same it displays a pop up saying that the song is already in this particular playlist. Same principle can be applied to the playlist I mentioned above.