[exim] processing forward file(s)

I have a local address "a" which forwards to another local address "b"
which forwards elsewhere.

If an email arrives to "b", it forwards.
If an email arrives to "a", it delivers to "b". In other words, the
system doesn't run thru the forwarding a second time to process the "b"
forward file.

Could someone suggest what router command would be preventing the
forward processing of the second addy? Thanks!

#
# normal/traditional dot.forward file for virtual addys
userforward_new:
   driver    = redirect
   require_files = 
/home/VIRTUAL/$domain/$local_part/.forward:ETCDIR/VIRTUAL/$domain/passwd
   condition = \

${lookup{$local_part}lsearch{ETCDIR/VIRTUAL/$domain/passwd}{yes}{no}}
   file      = /home/VIRTUAL/$domain/$local_part/.forward
   file_transport = address_file_gcust
   pipe_transport = pipe
   reply_transport = auto_reply
   user = mail
   no_verify
   no_expn
   check_ancestor
   allow_filter
   allow_fail