instead it worked well (publishing and uploading within few minutes) if i logged into the system as my_amuled_user through ssh and started it with 'amuled -f'
It makes no sense 
i agree, it is really inexplicable and probably someone will laugh about this, but it is the only way to make a kad (uploading only) amuled client working well on my system
Edit: what about su - my_amuled_user -c 'amuled -f'?
that i used is what is reported in the example init script
su $USER -c "$DAEMON -f"
http://www.amule.org/wiki/index.php/AMuleWeb#aMuled_and_aMuleWeb_as_servicesjust to clarify it is not a problem of starting the client or of permissions on the shared files, in both way amuled starts as user my_amuled_user, reads the same configuration files, loads the same shared files (show log in amulecmd reports 'loaded 505 shared files, etc), but publishing and uploading only works in the second way
however, hopefully my issue is solved with the patch of Gnucco
