What are you referring to normal playlists? The Bookmark lists? with the bookmarks you can add songs from SD and internal memory but i think the bookmarks get reset if you connect it to PC
Like if you have playlist created in MediaGo on your PC with songs which are not all in the same storage on your walkman.
E.g. you have tracks A,B,C,D on your Walkman in your internal storage and tracks F,G,H,I on your memory card.
If you now want to copy that playlist to your walkman's internal storage it will have songs F,G,H,I then transferred also into the internal storage and then you have them on your device twice. Or has this been solved in the ZX100?