[Exim] $thisaddress and pipe commands in filter files?

Is it just me or is the $thisaddress variable not expanded
when running a pipe command in a system filter?
I have a filter that contains a line like:

***
if foranyaddress $recipients
(${lookup{$thisaddress}lsearch{/etc/copy_rules}{$value}{}} is not "")
then
                unseen pipe "/usr/lib/sendmail $thisaddress"
endif
***

When the pipe command is executed then sender receives something like:

***
This message was created automatically by mail delivery software
(Exim).

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es)
failed:

  pipe to |/usr/lib/sendmail $thisaddress
    generated by message filter
    Child process of filter_pipe transport returned 1 from command:
    /bin/sh

The following text was generated during the delivery attempt:

------ pipe to |/usr/lib/sendmail $thisaddress
       generated by message filter ------

exim: neither action flags nor mail addresses given
***

It looks like the $thisaddress variable is expanded to an empty
string. Is it normal?