[PERDITION-USERS] Problem with managesieve AUTH PLAIN

Hi, I want to rewrite the username for authentication with managesieve. If I authenticate with "\0original_username\0password", then everything works fine, and perdition rewrites it to "\0rewritten_username\0password". Unfortunatly some clients including squirrelmail/avelsieve and roundcube send: "original_username\0original_username\0password", which gets rewritten to: "rewritten_username\0original_username\0password". It looks like dovecot and cyrus only care for the username after the first \0 which unfortunatly does not get rewritten via popmap. Micha Krause