[Exim] Sendmail requiring HELO again after RSET?

I received a user complaint yesterday due to sender verification
callouts failing thusly...

        220 mx2.communication.gc.ca ESMTP Sendmail (NO UCE) Official use only   8.12.10/8.12.10; Tue, 17 Feb 2004 15:16:55 -0500 (EST)
        HELO pentafluge.infradead.org
        250 mx2.communication.gc.ca Hello pentafluge.infradead.org      [213.86.99.235], pleased to meet you
        MAIL FROM:<>
        250 2.1.0 <>... Sender ok
        RCPT    TO:<pentafluge.infradead.org-1077049016-testing@???>
        550 5.0.0 <pentafluge.infradead.org-1077049016-testing@???>...  User unknown
        RSET
        250 2.0.0 Reset state
        MAIL FROM:<>
        503 5.5.1 Need HELO before MAIL

As far as I can tell, they're wrong to require another HELO, since I
already _said_ HELO, and RSET doesn't invalidate that. Is this a known
sendmail bug or could it be just this one broken installation?

--
dwmw2