FastFAT generates wrong short names

When dealing with accentuated names, FastFAT generates totally broken short names with illegal characters in.
"Menu Démarrer" gets "MENUD?~1" (illegal '?')
"Sélecteur de configuration clavier.lnk" gets "S?LECT~1.LNK" (illegal '?')

And when pushed to the limits:
"éèàùçeeauc.txt" gets "???>?E~1.TXT" (illegal '?', '>')