I have this odd problem that keeps cropping-up from time-to-time... I've been using an M3U playlist (just audio items) to keep track of music that I've been editing and copying, and my "Save Playlist" action has always been a right-click, select M3U from the file-types drop-down menu - Then double-click my playlist to over-rite.
Thing is, twice now, the playlist has been saved in an MLP format (ie: XML). Also, when opening an M3U list - The name of the file isn't shown on the blue top bar, still says "untitled"...