[Exim] problem with ${run expansion

Hi,

I'm trying to implement a check using the new SPF protocol (see
spf.pobox.com).

So, I have this acl in my exim.conf:

acl_check_mail:
   warn log_message =${run{/usr/bin/spfquery \
-ip=$sender_host_address -sender=$sender_address}{}{}}$value
         condition  = true
   accept

/usr/bin/spfquery is correctly installed and I can run it from a shell
as mail user, getting one or two rows at standard output, but it seems
exim fails executing it, and it doesn't return nothing.

I'm sure the acl is executed, and the command is well-build, because I
also tried with this:
acl_check_mail:
   warn log_message =/usr/bin/spfquery \
-ip=$sender_host_address -sender=$sender_address
   warn log_message =${run{/usr/bin/spfquery \
-ip=$sender_host_address -sender=$sender_address}{}{}}$value
         condition  = true
   accept

This way, I get the first log message, but not the second one.