simplexml_load_string の謎...

gistfile1.php

set_error_handler(function($errno, $errstr, $errfile, $errline) {  
    throw new \Exception($errstr, $errno);  
});  

try {
    $search = array("\0", "\x01", "\x02", "\x03", "\x04", "\x05","\x06", "\x07", "\x08", "\x0b", "\x0c", "\x0e", "\x0f");
    
    $options = array(
        'http' => array(
        'method' => 'GET',
        'header' => 'User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.94 Safari/537.36',
        ),
    );
    $context = stream_context_create($options);
    $xml_context = file_get_contents($rss_url, false, $context);
    $xml_context = str_replace($search, '', $xml_context);  
    
    if (mb_detect_encoding($xml_context, 'UTF-8', true) === false) { 
        $xml_context = utf8_encode($xml_context); 
    }

    if (strpos($xml_context, '<?xml', 0) === false){
        echo "×:Error:". $rss_url . "\n";
        continue 1;
    }
    
    $xml = simplexml_load_string($xml_context);
    if ($xml === false) {
        echo "Failed loading XML\n";
        foreach(libxml_get_errors() as $error) {
            echo "\t", $error->message;
        }
    }
    restore_error_handler(); //追記:2014.05.05  
} catch (Exception $ex) {
    restore_error_handler();  
    echo "×:Exception". $ex . "\n";  
    echo "×:Error:". $rss_url . "\n";
    continue 1;
}