[Exim] virtual users and .forward filters

Forgive me if the answer to this question is obvious, I have tried to find
the answer!

The situation is that I have a mix of "real" users on my box who have
shell accounts and proper home directories, as well as some "virtual"
users who just have mail accounts.

I have separate localuser & virtual_user routers and transports which all
works nicely. I also have a router setup for my real users that allows
them to use a .forward file to do move mail around into their IMAP
Maildirs as they like.

I would like to setup a similar thing for my virtual users, primarily so
that they can automagically filter mail marked as spam (via spamassassin)
into spam folders in their IMAP/Maildir store. I created two routers to
handle both in this order:

userforward:
driver = redirect
allow_filter
check_ancestor
check_local_user
directory_transport = address_directory
no_expn
file = $home/.forward
no_verify

virtual_userforward:
driver = redirect
allow_filter
check_ancestor
no_check_local_user
user = courier
group = mail
directory_transport = address_directory
no_expn
file = /home/virtual/$domain/$local_part/.forward
no_verify


However, when they are both in, only the virtual_userforward router works
(even though it's second in the list!), and I get errors for the
userforward router (i.e. when a real user receives mail) similar to:

2004-02-09 19:07:21 1AqGkR-0008Ml-7R == alex@???
R=virtual_userforward defer (-1): failed to stat
/home/virtual/mydomain.com/myuser/. (No such file or directory)

It seems to me that it's trying to deliver real users via the virtual
users transports...

Sorry it's gone on a bit, but does anyone have any ideas? Perhaps it would
be better to define a system wide filter to move spam messages to spam
folders, but I would ideally like the capabilioty for run virtual user
.forward files as well.

Many, many thanks in advance!

--Alex