Есть такой параметр в php.ini
variables_order = "EGPCS"
а означает он следующее:
; This directive describes the order in which PHP registers GET, POST, Cookie,
; Environment and Built-in variables (G, P, C, E & S respectively, often
; referred to as EGPCS or GPC). Registration is done from left to right, newer
; values override older values.