; - allow_call_time_pass_reference = Off [Code cleanliness]
; It's not possible to decide to force a variable to be passed by reference
; when calling a function. The PHP 4 style to do this is by making the
; function require the relevant argument by reference.
credo che sia per questo. si trova nel php.ini

un'occhiata al manuale:

http://www.php.net/manual/it/language.functions.php
http://www.php.net/manual/it/language.references.php