I did a lot of code fixing on the playlist a while ago. There existed a bug that after adding entries, if you changed web admin pages, those changes were lost. By just closing the web browser after editing the playlist, everything would stay as it should. There were also a couple of other bugs that would discard changes.
Of course, this is fixed in SVN now. If you want the new playlist editor changes (there are a ton of changes/bug fixes) follow the instructions here:http://forum.linuxmce.org/index.php?topic=5666.msg33260