It's not a bug, it's just that the origin isn't POSTMASTER@nodeid, it's
undetermined (typical cause: MAILER bug causing it to omit the whole
header, with only the first 'Received:' line being sent). Seeing that the
origin is undetermined, LISTSERV puts POSTMASTER in the outgoing 'From:'
field, because you've got to have a 'From:' field with something valid in
it.
Eric