If you do not use header() in your php script, what are the default http headers your browser gets? Here are the http headers php 5.4 generates in the response:
Date: Mon, 17 Nov 2014 11:39:44 GMT\r\n
Server: Apache/2.4.9 (Win32) OpenSSL/0.9.8y PHP/5.4.27\r\n
X-Powered-By: PHP/5.4.27\r\n
Content-Length: 13\r\n
Keep-Alive: timeout=5, max=99\r\n
Connection: Keep-Alive\r\n
Content-Type: text/html\r\n
You can get this http headers information using Wireshark.