This shouldn't be a problem for you, use a linux live-cd...
If I have a file called canción, without any extension, and I want to
rename it to poesía, without extension, it doesn't do it...
It only works if the filename has at least 8 characters including point and extension. Moreover, if the $to filename, has equal or more number of characters
than the $from filename and this has at least 10 characters, strange
characters appear on the $to filename.
Windows related problems I bet... avoid yourself a lot of trouble and try linux for this specific task