To make it possible to undo the change of filenames, the old names are stored as a comment (filenote) in the according file (the file itself is not changed, but any old filenotes will be changed). If you do not want to change the filenotes, you may disable this function by deselecting the undo-gadget in the settingswindow. The filenotes will then be kept, but it will not be possible to give the their old names (easily).