Claudio_ch,
I'm not sure I understood your problem. Calibre's handling of author names can be a bit confusing though.
If you would like to change how calibre works, read the
Tweaks section of the calibre manual. Most likely you will want to look at the Author Sort Name Algorithm.
There are several topics on this subject here in the forums, which you can find by looking for "fn ln" in the search field. You could also try looking for "author name" or "author_sort". Many of the results will be about your issue.