[exim] Duplicates aren't eliminated for domains in local_dom…

Hello,

Yet another problem appeared: there are lines in exim.conf:

From: /etc/exim.conf

================== exim.conf snippet below
primary_hostname = example.com
domainlist local_domains = @ : example.ru : example.local : localhost
: localhost.localdomain

# From routers: system_aliases

system_aliases:
driver = redirect
allow_fail
allow_defer
data = ${lookup{$local_part}lsearch{/etc/aliases}}
check_ancestor = true
file_transport = address_file
pipe_transport = address_pipe

================== exim.conf snippet above

In /etc/aliases:

userlist: user1,userlist

Scenario 1: a message is sent like this:

To: userlist@???
Cc: user1@???

Result: user1 receives one copy of the message (duplicates eliminated)

Scenario 2: a message is sent to any domain from local_domains, i.e. like this:

To: userlist@???
Cc: user1@???

Result: user1 receives 2 copies of the inbound message (duplicates not
eliminated).

In <exim logs root>/main.log I see the following lines:

2008-05-13 15:33:24 1Jvpwq-0004Ls-3D <= user1@???
H=diamond.local [10.1.0.54] P=esmtpsa X=TLSv1:AES256-SHA:256
A=PLAIN:user1 S=639 id=48295251.9090905@???
2008-05-13 15:33:24 1Jvpwq-0004Ls-3D => userlist <userlist@???>
R=procmail T=procmail
2008-05-13 15:33:24 1Jvpwq-0004Ls-3D => user1 <userlist@???>
R=procmail T=procmail
2008-05-13 15:33:24 1Jvpwq-0004Ls-3D => user1 <user1@???>
R=procmail T=procmail
2008-05-13 15:33:24 1Jvpwq-0004Ls-3D Completed

May I ask how should I enable duplicates elimination if the target
domain is in in local_domains, but not equal to primary_domain?

Thanks.