Hi
I listen to music a lot and make extensive use of the Smart Playlists.
It seems that when I update the filters on an existing smart playlist and click UPDATE I finish up with duplicate playlist, As best I can work out one is the original, the other is the one with the updated filters. The process repeats if I do it again.
I remember an issue with another user who used a very high number of search arguments.
With the result that at some point the generated URL that was passed to the server became too long and was (probably) truncated, resulting in unexpected behaviour.