[horde] Horde spamming syslog

[Arjen de Korte]

Since last Friday, Horde is spamming my syslog with messages like

Mar 10 21:30:10 mail horde: [imp] Login success for arjen (Horde user  
arjen) [192.168.1.126] to {localhost:143 [imap]} [pid 3574 on line 183  
of "/srv/www/htdocs/horde/imp/lib/Auth.php"]

Looking at this, messages should be logged with either level NOTICE or  
INFO. This is weird, since I configured logging for level WARNING:

   $conf['log']['priority'] = 'WARNING';
   $conf['log']['ident'] = 'horde';
   $conf['log']['name'] = LOG_LOCAL7;
   $conf['log']['type'] = 'syslog';
   $conf['log']['enabled'] = true;

Since both NOTICE and INFO are lower than WARNING, these messages  
should never have made it to the syslog. Looking at the timestamps,  
they seem to coincide with ActiveSync activity. Any ideas?