[Exim] Exim 4.14 problem

I am using a POP/IMAP-before-SMTP solution to authorize users to relay
mail. I have:

acl_smtp_rcpt = check_recipient
hostlist relay_hosts = ... : /path/to/relay/hosts/file : ...
...
begin acl
check_recipient:
    ...
    accept hosts = +relay_hosts
    ...

Some ISPs provide reverse DNS but not forward DNS (or at least not
forward DNS for the reverse DNS name). When one of these users checks
mail, their hostname (from reverse DNS) is listed in the
/path/to/relay/hosts/file. When Exim checks the hostlist, it gets to
the "bad" hostname (that doesn't resolve) and then fails the check
without trying to resolve any of the hostnames after that. So
legitimate relay users who happen to be listed after the "bad" hostname
are denied access.

Can this be fixed? Does Exim 4.20 fix it already? (I'll probably put a
gethostbyname() check into my POP-before-SMTP process anyway.)

Thanks,
John Dalbec