I was renaming files with exfalso, and while it was still working, I
moved away the folder.
Exfalso said something about not being able to modify certain tags on
the file because it's "not supported by the file type"; but actually it
just couldn't rename the file because it was no longer there...

P.S. exfalso also clearly shows O(n*n) or worse performance when
renaming files. It seems that after each file it has renamed, it rereads
the directory contents, recomputes all the 'new' filenames in the
display and updates the displayed information.
When the list of selected files gets shorter (because it has already
renamed a lot of them), it gets faster and faster.
Just try running exfalso's renaming function on a larger directory, and
you might be able to easily reproduce it.
Debian Release: lenny/sid
  500 unstable        www.debian-multimedia.org
  500 unstable        ftp.de.debian.org
    1 experimental    ftp.de.debian.org
--- Package information. ---
Depends                (Version) | Installed
================================-+-=============
python-central        (>= 0.5.8) | 0.5.15-0.1
python                  (>= 2.4) | 2.4.4-6
python-ctypes                    | 1.0.2-2
python-mutagen          (>= 1.8) | 1.11-1
python-gtk2             (>= 2.8) | 2.12.1-1
libgtk2.0-0         (>= 2.8.8-1) | 2.12.3-2
python-pyvorbis                  | 1.3-1.2
libmpcdec3                       | 1.2.2-1

best regards,
Erich Schubert
-- 
   erich@(vitavonni.de|debian.org)    --    GPG Key ID: 4B3A135C    (o_
     This one's tricky. You have to use imaginary numbers, like     //\
                      eleventeen... --- Hobbes                      V_/_
            Es lohnt sich nicht, die Augen aufzumachen,
                   wenn der Kopf im Sand steckt.