[exim] option "interface" in smtp transport and ipv6

Hello!

I've set up smtp transport in this way:
external_smtp_batv:
                driver          = smtp
                return_path     = ${prvs {$return_path}{BATVKEY}}
                dkim_domain     = +local_domains
                dkim_selector   = 100623
                dkim_private_key= /etc/ssl/poczta.cibet.pl.key
                dkim_canon      = relaxed
                interface       =
${lookup{$domain}lsearch{/etc/exim/domeny_interfejs.txt}{$value}{}}

If recipient domain is found in appropriate file and destination mx
doesn't have AAAA records everything works correctly. Problem appears
when dest. mx has AAAA, then option "interface" is ignored and mail is
sending using ipv6 proto.
It looks there is bug in smtp tranposrt or option "interface" should
named "interface_ipv4".
Regards,
Marcin