I am having a similar problem. I am running version 1586 on a NSLU2. The playlist was created the first time using a copy of the windows iTunes Music Library.xml file (from version 126.96.36.199) placed in the NSLU music folder.
Now when I change the playlist in itunes and then recopy the file to the NSLU2 it stays the same as the first playlist I loaded in.
I have rescanned a number of times both full and regular. I have stopped the server and restarted it. No change to the playlists.