I use php 7.0.0 with symfony 3.1.8. The issue is when I got errors from php - symfony doesn't return me stack trace, all I can see is "Internal Server Error" page. In logs of apache I found FastCGI: comm with server "/Applications/MAMP/fcgi-bin/php7.0.0.fcgi" aborted: error parsing headers: duplicate header 'Content-Type'
I started debugging, and that's what I found. I use php scalar type hinting, so when the wrong type comes as argument, php returns TypeError, symfony catches it, and then step by step:

1. Symfony\Component\Debug\ErrorHandler:handleException
   call_user_func($this->exceptionHandler, $exception) L:546
2. Symfony\Component\Debug\ExceptionHandler:handle
   $this->sendPhpResponse($exception); L:121
3. Symfony\Component\Debug\ExceptionHandler:sendPhpResponse
   header('Content-Type: text/html; charset='.$this->charset); L:173 - which sends me header of content type first time.
4. Symfony\Component\Debug\ExceptionHandler:handle (continue)
   call_user_func($this->handler, $exception); L:144
5. Symfony\Component\HttpKernel\HttpKernel:terminateWithException
   $response->sendHeaders(); L:104
6. Symfony\Component\HttpFoundation\Response:sendHeaders
   header($name.': '.$value, false, $this->statusCode); L:339 - which sends me header of content type second time.

The output of headers_list function:
0 = "X-Powered-By: PHP/7.0.0"
1 = "Content-Type: text/html; charset=UTF-8"
2 = "Cache-Control: no-cache"
3 = "X-Debug-Token: 242fbb"
4 = "X-Debug-Token-Link: http://pr.project/app_dev.php/_profiler/242fbb"
5 = "Content-Type: text/html; charset=UTF-8"
6 = "Date: Sun, 08 Jan 2017 18:45:04 GMT"

Which causes error of duplicating headers.
Please fix.