I got trouble with web browsers buffering (not chaching).
I call this php script :
sleep(5); echo \'1st step\'; echo (str_repeat(\' \',256)); sleep(5
Oh, I guess I need to make the answer an answer, not a comment, so you can accept it.
The HTML5 charset sniffing buffer size is 512 bytes. So the response needs to either have 512 bytes of padding or set a charset (via <meta> tag or HTTP header).
<meta>