Shopware error Uncaught exception 'Zend_Controller_Response_Exception' with message 'Cannot send headers; headers already sent in, line 0'

Question

I freshly installed the shopware php framework 5.1.5 (new DB, new files). But when I like to change something in the backend and press save then I get the following error: PHP Fatal error: Uncaught exception 'Zend_Controller_Response_Exception' with message 'Cannot send headers; headers already sent in , line 0'

I know that the normal cause of this error is when a character before the header is sent. But in this case I have line '0' and when I look at the file "Abstract.php" the tag "{?php" is correct (no characters before, encoding looks fine) and at the end of the file no closing tag is there.

Any ideas what it else can be or how I can nail the problem down? Thx

PHP Fatal error:  Uncaught exception 'Zend_Controller_Response_Exception'   with message 'Cannot send headers; headers already sent in , line 0' in /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Zend/Controller/Response/Abstract.php:323
Stack trace:
#0 /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Zend/Controller/Response/Abstract.php(115): Zend_Controller_Response_Abstract->canSendHeaders(true)
#1 /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Enlight/Controller/Plugins/Json/Bootstrap.php(123): Zend_Controller_Response_Abstract->setHeader('Content-type', 'application/jso...', true)
#2 [internal function]: Enlight_Controller_Plugins_Json_Bootstrap->onPostDispatch(Object(Enlight_Controller_ActionEventArgs))
#3 /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Enlight/Event/Handler/Default.php(91): call_user_func(Array, Object(Enlight_Controller_ActionEventArgs))
#4 /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Enlight/Event/EventManager.php(213): Enlight_Event_Handler_Default- in /var/www/vhosts/skate.ch/dev.skate.ch/shop/engine/Library/Zend/Controller/Response/Abstract.php on line 323

Answer 1

I could solve the problem. The cause was another error resp. a "warning" which I thought first it is not important and can be ignored.

[20-Aug-2016 11:04:26 CET] PHP Deprecated:  Automatically populating $HTTP_RAW_POST_DATA is deprecated and will be removed in a future version. 
To avoid this warning set 'always_populate_raw_post_data' to '-1' in php.ini and use the php://input stream instead. in Unknown on line 0

After I entered in the php.ini the following setting the error regarding the headers disappeared.

 always_populate_raw_post_data=-1

It looks like that the Warning regarding $HTTP_RAW_POST_DATA is sent to std output before the headers get sent, which then produces of course the error regarding the headers.