Duplicate Entries in database

Hi!

I'm trying to use RoundCube, but I have a problem: every time a user log in and modify an option (language, identities...), in the database appear a new entry for him. In this way I have duplicate entries for every user, and the saved options are not used the next time the user log in, because he is took back to the first entry (the one with no options set).

I think that modifying the db using the complete email address (user@domain.tld) as user_id could solve the problem...

Thank you for any help, and please insert my email address in your replies, since I'm not in the mailing list. Paolo