TYPO3 Core

To files has to be changed

1) class.tslib_content.php

change line 5193 $page = $GLOBALS['TSFE']->sys_page->getPage($link_param,$disableGroupAccessCheck);

to

$page = $GLOBALS['TSFE']->sys_page->getPage($link_param,$disableGroupAccessCheck,TRUE);

(a third parameter is added for getPage)

2) class.t3lib_page.php

Line 184ff
Change the function get Page and add the function checkPage

/**
 * Returns the $row for the page with uid = $uid (observing ->where_hid_del)
 * Any pages_language_overlay will be applied before the result is returned.
 * If no page is found an empty array is returned.
 *
 * @param    integer        The page id to look up.
 * @param    boolean        If set, the check for group access is disabled. VERY rarely used
 * @param     boolean        If set, the check will include the rootline
 * @return    array        The page row with overlayed localized fields. Empty it no page.
 * @see getPage_noCheck()
     /
    function getPage($uid, $disableGroupAccessCheck=FALSE,$userRootlineCheck=FALSE)    {
        $res = $GLOBALS['TYPO3_DB']->exec_SELECTquery('', 'pages', 'uid='.intval($uid).$this->where_hid_del.($disableGroupAccessCheck ? '' : $this->where_groupAccess));
        $row = $GLOBALS['TYPO3_DB']->sql_fetch_assoc($res);
        $check = ($userRootlineCheck ? $this->checkPage($uid) : 1 );
        if ($row && $check){
            $this->versionOL('pages',$row);
            if (is_array($row))        return $this->getPageOverlay($row);
        }
        return Array();
    }

/**
 * Checks the current rootline for defined sections.
 *
 * @param    integer        The page id to look up.
 * @return    boolean        
     */

function checkPage($uid)    {
        $MP = t3lib_div::_GP('MP');
        $rootLine = $this->getRootLine($uid,$MP);
        $c=count($rootLine);
        while(list($k,$page) = each($rootLine)){
            if($page['title']=='Seminare'){
                if ($page['extendToSubpages'] && !$GLOBALS['TSFE']->checkEnableFields($page)) {
                    return false;
                }    
            }
        }
        return true;
    }

confirmed for 4.3, please take a look at the duplicate issues for a "how to reproduce"