Win XP SP3 (I know) on NTFS volume: Took a little while to suss - well, cure this at least. I use the label colours function to indicate the status of songs I'm writing, eg 'In Progress', 'Finished', 'Pants', etc. I also use the DOpus RTF viewer to edit, so all files are in .RTF format. One song in particular, called 'How Close We Nearly Came', lost its label every time I clicked the 'save' button - whether it had been altered or not. Didn't happen to any other song, with any other label, but even if I deleted the label and restored it, or used a label that worked fine on any other song file, the label wouldn't stick to that file - UNTIL I unchecked the 'enable label storage in the file system' preference. Now it behaves as expected. There are other songs with longer titles, so I don't know why this should happen, but I wonder if anyone else has had the same. Btw, the folder path is as follows: D:\Home\My Music! 2014\Song List\My songs\ 
And of course, now I can't reproduce it...