Greetings alec,
My db_dsnw isn't empty or wrong :
$rcmail_config['db_dsnw'] = 'mysql://***:***@sql.franceserv.fr/***';
(i have masked the login, password and database).
I have checked with Roundcube 0.8.5 and it's exactly the same line, so it's not a problem of "db_dsnw".
Someone to check this bug please ?