Renaming Song Titles on SX900 Playlists

[ChrisH]

I have quite a few entries the the Bonus SX900 Playlist file that has unknown song titles that really suit other songs so I tried to rename the title so it's easy to find.  I start off great and select the song then touch "edit" and "rename" and use the on screen keypad to change the song title .. However when I touch "save" it doesn't want to save to the USB and keeps saying "playlist has changed" ... if I touch "cancel" I lose the entire folder and have to pull the usb out and reconnect and of course the old song name is back there as it never saved.   Once I have renamed the song title ..what is the procedure to save the new name to the USB please??