[Exim] smartuser problem

I have a director like this:

redirect_aliases:
driver = smartuser
domains = DCS_DOMAINS
local_parts = lsearch;/etc/mail/redirect_aliases
new_address = :fail: user has moved; please try <${lookup{$local_part}lsearch{/etc/mail/redirect_aliases}{$value}}>
suffix = /*
suffix_optional
verify_only

..but it looks like (with exim -d11 -bv) Exim fails to strip a suffix (if
supplied), and unfortunately the message is picked up by a subsequent
director.

It works for an address without a suffix, and I have another similar
smartuser director (using condition = .. rather than local_parts = ..)
which behaves as I'd expect wrt suffixes.

Am I doing something wrong? It is a Friday afternoon.

Matt