IP address changes on its own?

just a quick addition - its my base url that is changing automatically on its own.

no idea how its happening.  it literally works for a few days then starts handing out the internal IP again.  i've tried cleaning the cache once i change it back but it still happens.  how do i look to see if there isa "cron job" (no idea what that is

i'm the only admin.  its a vanilla system - i havnt made any changes.  thanks for the help!

this is part of the admin file:

--------
if (isset($_POST['form_sent']))
{
    // Custom referrer check (so we can output a custom error message)
    if (!preg_match('#^'.preg_quote(str_replace('www.', '', $pun_config['o_base_url']).'/admin_options.php', '#').'#i', str_replace('www.', '', (isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : ''))))
        message('Bad HTTP_REFERER. If you have moved these forums from one location to another or switched domains, you need to update the Base URL manually in the database (look for o_base_url in the config table) and then clear the cache by deleting all .php files in the /cache directory.');

    $form = array_map('trim', $_POST['form']);

    if ($form['board_title'] == '')
        message('You must enter a board title.');

    // Clean default_lang
    $form['default_lang'] = preg_replace('#[\.\\\/]#', '', $form['default_lang']);

    require PUN_ROOT.'include/email.php';

    $form['admin_email'] = strtolower($form['admin_email']);
    if (!is_valid_email($form['admin_email']))
        message('The admin e-mail address you entered is invalid.');

    $form['webmaster_email'] = strtolower($form['webmaster_email']);
    if (!is_valid_email($form['webmaster_email']))
        message('The webmaster e-mail address you entered is invalid.');

    if ($form['mailing_list'] != '')
        $form['mailing_list'] = strtolower(preg_replace('/[\s]/', '', $form['mailing_list']));

    // Make sure base_url doesn't end with a slash
    if (substr($form['base_url'], -1) == '/')
        $form['base_url'] = substr($form['base_url'], 0, -1);

    // Clean avatars_dir
    $form['avatars_dir'] = str_replace("\0", '', $form['avatars_dir']);

    // Make sure avatars_dir doesn't end with a slash
    if (substr($form['avatars_dir'], -1) == '/')
        $form['avatars_dir'] = substr($form['avatars_dir'], 0, -1);

    if ($form['additional_navlinks'] != '')
        $form['additional_navlinks'] = trim(pun_linebreaks($form['additional_navlinks']));

    if ($form['announcement_message'] != '')
        $form['announcement_message'] = pun_linebreaks($form['announcement_message']);
    else
    {
        $form['announcement_message'] = 'Enter your announcement here.';

        if ($form['announcement'] == '1')
            $form['announcement'] = '0';
    }

    if ($form['rules_message'] != '')
        $form['rules_message'] = pun_linebreaks($form['rules_message']);
    else
    {
        $form['rules_message'] = 'Enter your rules here.';

        if ($form['rules'] == '1')
            $form['rules'] = '0';
    }

    if ($form['maintenance_message'] != '')
        $form['maintenance_message'] = pun_linebreaks($form['maintenance_message']);
    else
    {
        $form['maintenance_message'] = 'The forums are temporarily down for maintenance. Please try again in a few minutes.\n\n/Administrator';

        if ($form['maintenance'] == '1')
            $form['maintenance'] = '0';
    }

    $form['timeout_visit'] = intval($form['timeout_visit']);
    $form['timeout_online'] = intval($form['timeout_online']);
    $form['redirect_delay'] = intval($form['redirect_delay']);
    $form['topic_review'] = intval($form['topic_review']);
    $form['disp_topics_default'] = intval($form['disp_topics_default']);
    $form['disp_posts_default'] = intval($form['disp_posts_default']);
    $form['indent_num_spaces'] = intval($form['indent_num_spaces']);
    $form['avatars_width'] = intval($form['avatars_width']);
    $form['avatars_height'] = intval($form['avatars_height']);
    $form['avatars_size'] = intval($form['avatars_size']);

    if ($form['timeout_online'] >= $form['timeout_visit'])
        message('The value of "Timeout online" must be smaller than the value of "Timeout visit".');

    while (list($key, $input) = @each($form))
    {
        // Only update values that have changed
        if (array_key_exists('o_'.$key, $pun_config) && $pun_config['o_'.$key] != $input)
        {
            if ($input != '' || is_int($input))
                $value = '\''.$db->escape($input).'\'';
            else
                $value = 'NULL';

            $db->query('UPDATE '.$db->prefix.'config SET conf_value='.$value.' WHERE conf_name=\'o_'.$db->escape($key).'\'') or error('Unable to update board config', __FILE__, __LINE__, $db->error());
        }
    }

    // Regenerate the config cache
    require_once PUN_ROOT.'include/cache.php';
    generate_config_cache();

    redirect('admin_options.php', 'Options updated. Redirecting …');
}

$page_title = pun_htmlspecialchars($pun_config['o_board_title']).' / Admin / Options';
$form_name = 'update_options';
require PUN_ROOT.'header.php';
---------

nope.  i'm the only one with access.  i've even checked my firewall logs.  this is happening even with no-one accessing the forum but me.  it must be picking it up from somehwere.

i havnt modified any code at all. its all vanilla.  the backups are set to run so i'll take that off and see if it helps.  the IP has changed again since i corrected it last night.  i can guarnatee no-one else is changing it as i've put a rule on the fw saying only i can access it. 

can one of you guys check my admin options file i posted above?  i dont have the ip in there?  maybe i've go a line missing?  really appreciate your help on this!

cheers

yemgi: Vanilla, as in plain, unmodified

smartys - can you copy in the paragraph in the admin-options.php file that has the base url?