Filenames constantly changing

I'm using Filefield Paths 1.4 and we are using it to prepend 'mdv-' to the front of every mp3 file that is uploaded. However, when the nodes get edited sometimes mdv is prepended again resulting in files that are of the form mdv-mdv-[filename], which wouldn't be an issue except Drupal still thinks the files are at mdv-[filename].