[Exim] .forward files and suffixes

i've made my exim able to receive username+suffix
i've chosed + as the seperator, and this part works.

How ever, i wish to use .forward files as an exim filter
and sort the messages based on the part after the +

This is part of my DIRECTOR CONFIG
userforward:
suffix = +*
suffix_optional = yes
driver = forwardfile
require_files = ${home}
directory_transport = address_directory
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply
no_verify
check_ancestor
file = .forward
modemask = 002
filter


# this director matches username+extension@???

extension:
suffix = +*
suffix_optional = yes
driver = localuser
transport = maildir_delivery



But it doesnt work, when i try to test on the
$local_part_suffix, or prefix, they are empty
(also when i write them out in the logfile)
Even for the builtin real-$USER (default debian
exim config.)

intranet:/etc/exim# exim -bV
Exim version 3.31 #1 built 19-Jul-2001 00:41:24
Copyright (c) University of Cambridge 2001





ion++