[exim] "unseen" not working correctly?

Hello!

I have two routers in a row that serve the purpose of forking a copy of
a mail to one system while delivering the very same mail to another
system, too. I need this for testing a system without affecting the real
mail flow.

The routers are simple manualroute routers with fixed destinations. The
only option set is 'same_domain_copy_routing' to speed up things: the
system is the main entry point to a mid-volume enterprise system and I
do not rely on the local part at all. They get fed mails based on
decision earlier routers take, so no decision is needed on these two -
we know what we got. These are the routers in question:

external_copy:
driver = manualroute
condition = yes
transport = external_smtp
route_data = 192.168.1.20
same_domain_copy_routing
unseen = yes

external:
driver = manualroute
transport = external_smtp
route_data = 192.168.1.1
same_domain_copy_routing

This is the transport both use:

external_smtp:
driver = smtp
interface = 192.168.1.100
tls_certificate = /some/file
tls_privatekey = /some/otherfile
no_tls_tempfail_tryclear
hosts_randomize = true

The problem I encounter is: The first router gets a mail with, say, 13
recipients to process, whereas the second router only gets fed 7
recipients afterwards. I understood the 'unseen' option as follows: The
second router should get a 100% copy of the mail the first one got. I.
e., no matter wether the first router is successful in delivering or
not, the addresses are in every case given to the second router. Am I
wrong in that point?

If I am wrong, how could I implement forking away a copy of each email
to a different host? I guess a shqdow_transport is not what I need?

I'm running a self-compiled exim 4.71 on a minimized Debian Lenny
system. Compile options are available, for sure.

Any help would be greatly appreciated.

With highest regards,

Robert Kehl