Its strange and drives me crazy. It happened before and after the GDR updates. I have tried a couple of factory resets but it still happens. Not just with music either, photos in the camera roll double and triple out of nowhere. I say triple but actually there is up to 20 of the same photo showing in my camera roll! There is only one real copy of the file though so it seems like some kind of database or thumbnail problem I don't know.
I was trying to find out if this happens to the 1020 but I cant find any real info. I found this that shows the problem happening to a range of other Lumia's. Lots of comments below on the same problem.
https://windowsphone.uservoice.com/...t-an-idea-but-a-bug-pictures-music-and-video-
Other issue is if I remove a music file from the phone (using my PC) then it doesn't update in the music player. It still lists the track and gives an error if its played. Even turning it on and off it never refreshes the music list. so the list gets bigger and bigger with loads of dead links. It seems like WP8 has a very odd file system. I have Windows 8 on my PC so it should really have no issues copying files to a Win 8 phone.
If this happened to any potential 1020 I bought I would be very unhappy. I wrote a post in the 1020 forum (because Im thinking of getting one) but it was removed, I guess they don't want to speak about negatives there!
But if you say its ok for you then that's a start..