why is $_REQUEST empty

if your post body larger than post_max_size or upload_max_filesize which in the php.ini may be cause $_POST and $_REQUEST empty too.

Also try check "request_order" option in php.ini:

; This directive determines which super global data (G,P,C,E & S) should
; be registered into the super global array REQUEST. If so, it also determines
; the order in which that data is registered. The values for this directive are
; specified in the same manner as the variables_order directive, EXCEPT one.
; Leaving this value empty will cause PHP to use the value set in the
; variables_order directive. It does not mean it will leave the super globals
; array REQUEST empty.
; Default Value: None
; Development Value: "GP"
; Production Value: "GP"
; http://php.net/request-order
request_order = "GP"