[exim] smtp transport uses wrong server

Hi

I have the following:

Several DIFFERENT systems are listening on port 25 on 127.0.1.1, 127.0.2.1,
127.0.3.1.

I have a router that does basically the following:

myrouter:
driver = accept
transport = server
address_data = ${...some lookup yielding 1, 2 or 3...}

server:
driver = smtp
hosts_override = true
hosts = 127.0.$address_data.1
interface = 127.0.0.1
allow_localhost = true

This works for mails, which have one recipient.
However if a mail has more then one recipient and they have different
destination systems, they are both routed to the first server.
exim then simply ignores the value of host for the second call of transport
server.

Is this a bug?
What can I do ?

Regards,
Steffen