Allowed memory size exhausted (xcache.php)

Good day, gentlemen.

I use authcache + cacherouter with xcache engine enabled. Multisiting is enabled too, so both mysite/settings.php and default/settings.php have this snippet:

<?php 
$conf['cache_inc'] = './sites/all/modules/authcache/authcache.inc';
$conf['cache_inc_via_authcache'] = './sites/all/modules/cacherouter/cacherouter.inc';

$conf['cacherouter'] = array(
  'default' => array(
    'engine' => 'xcache',
    'servers' => array(),
    'shared' => TRUE,
    'prefix' => '',
    //'path' => 'sites/default/files/filecache',
    'static' => FALSE,
    'fast_cache' => FALSE,
  ),
);?>

The problem is:
Authcache and cacherouter seem to do their work well, but I recieve in my error_log every 10-30 minutes this message:

(mod_fastcgi.c.2701) FastCGI-stderr: PHP Fatal error:  Allowed memory size of 536870912 bytes exhausted (tried to allocate 262144 bytes) in /var/www/sites/all/modules/cacherouter/engines/xcache.php on line 100

memory_limit in php.ini is set to 512M. I rose it twice from 64M to 512M with the only effect: error repeats rarely, but still it occurs. It seems like on line 100 there something causing a memory leak ;)

--------------------------------------

XCache configuration:

Lighttpd and php-cgi

# php-cgi -v
PHP 5.2.13 (cgi-fcgi) (built: Mar 21 2010 16:04:16)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies
    with XCache v1.3.0, Copyright (c) 2005-2009, by mOo

# lighttpd -v
lighttpd/1.4.28 - a light and fast webserver
Build-Date: Oct 24 2010 15:58:28

Server configuration:

Slackware 13.1 x86_64
4 Core (8 as of HT) Xeon 5620
12 Gb DDR3

all server software is 64 bit.