Is there anyone with some knowledge about the media player around here?

I have many audio files that I listen to through the media player. I created playlists in the .m3u file format. It works great, the media player finds them and they're accessable in the software, or if I execute the m3u file alone it opens in the software, no problems...totally expected action... except:
-This morning I edited a song in a playlist. The media player duplicated the playlist capitalizing the first letter in the duplicated file. I can't figure out where this new file is located. It did it a few hours later with another playlist that I didn't edit. Anyone have a suggestion(s)? Searching with find -i doesn't turn up anything.
-I have one playlist, seriously 1 from 300, that the media player doesn't recognize, and hasn't recognized for a year.

Where might the mediaplayer be storing files?