A couple of readers wrote in with suggestions to fix this problem (described previously). None of the tips worked for me, but in the course of checking them out, I tripped over something that did work: After entering the text and closing the Get Info window, immediately select to Eject (not Put Away) the disk. If it works the same for you as it did for me, a message should then appear asking you to reinsert the disk. Do so. At this point, your comments are saved and will now not be deleted when you later unmount the disk.