I've always used the Transliteration module on d6 with no problems.
I installed it on the new site on d7 and I have this situation.

The original file name with space and underscore:
name of_file.doc

After loading I have the correct version with two underscores:
name_of_file.doc

After saving I get the words linked into one:
nameoffile.doc

The result is terrible, just look here:
http://www.iismarchesi.it/gov/
http://www.iismarchesi.it/gov/bacheca-sindacale

What might be the cause?

Thanks