当前字符集：utf8作为响应

Question

Where is the debug information "Current character set: utf8" comming from?

It appears always first when I echoing something within my index.php (slim) script.

I really become desperate trying to suppress this.

May it caused by the .htaccess rules?

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ %{ENV:BASE}index.php [QSA,L]

Here my setting:

Server: Apache/2.4.9 (Win32) OpenSSL/1.0.1g PHP/5.5.11 X-Powered-By: PHP/5.5.11 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124 Safari/537.36

The relevant section of the index.php:

function echoRespnse($status_code, $response) {
$app = \Slim\Slim::getInstance();
// Http response code
$app->status($status_code);
$app->config('debug', false);

// setting response content type to json
$app->contentType('application/json');
//$app->response()->header('Content-Type', 'application/json');

echo json_encode($response);
}

Any help would be greatly appreciated