[exim] $domain_data not populated, caching problem?

When I try to use $domain_data from a redirect router
the value seems to unpopulated:

  aliases:
          driver = redirect
          domains = +local_domains
          data = ${lookup{$local_part}lsearch*{CONFDIR/aliases/$domain_data}}
          qualify_preserve_domain
          allow_fail
          allow_defer
          forbid_file
          include_directory = CONFDIR
          pipe_transport = address_pipe

Debug output:

233304 --------> aliases router <--------
233304 local_part=lollipopman domain=wikimedia.org
233304 checking domains
233304 cached yes match for +local_domains
233304 cached lookup data =
233304 wikimedia.org in "+local_domains"? yes (matched
"+local_domains" - cached)
233304 calling aliases router
233304 rda_interpret (string):
'${lookup{$local_part}lsearch*{/etc/exim4/aliases/$domain_data}}'
233304 search_open: lsearch "/etc/exim4/aliases/"
233304 aliases router: defer for lollipopman@???
233304 message: failed to expand
"${lookup{$local_part}lsearch*{/etc/exim4/aliases/$domain_data}}":
/etc/exim4/aliases/ is not a regular file (lsearch lookup)

Is this possibly a caching bug like this one, mentioned many years ago,
https://exim-users.exim.narkive.com/MUiNGYww/bug-in-domain-data-caching?

Or is there something silly that I am missing?

Thanks, Jesse