Current implementation of add_to_log() updates user lastaccess field by issuing the next instruction:

$res = $db->Execute('UPDATE '. $CFG->prefix .'user
SET lastip=\''. $REMOTE_ADDR .'\', lastaccess=\''. $timenow .'\'
WHERE id = \''. $userid .'\' AND '.$timenow.' - lastaccess > 60');

This method doesn't take care of registry caché. update_record() should be used to update that fields.

One of the actual problems has to do with messaging subsystem and email notifications being sent because of inconsistency of rcache.

Thanks in advance