Apache closes connection at variable assignment

Hi PHP-Cracks! I'm contacting you now because I'm in need of professional PHP help. I've opened a question over at Stack Overflow (http://stackoverflow.com/questions/33394717/zero-sized-reply-php-crashing-on-variable-assignment). I don't have any clue, why the server would either crash or close the connection on a simple variable assignment. Detailed, this means: Adding a string in an array which is a class property (see the question for more details). I hope, some of you may have experienced similar problems and are able to locate the cause a bit more than it is now. Thanks in advance!! -Florian