Message-IDs on Usenet gateway

[Random832]

Dave Farrance <df at see.replyto.invalid> writes:
> That raises another question.  I'm seeing a number of broken threads
> because people reply to posts that are not present in Usenet.  It's not
> just my main news-server because my newreader can gather posts from
> several Usenet servers and those posts are nowhere on Usenet.
>
> Case in point:  The post by Terry Reedy quoted above, reference
> <n3t7jo$ae3$1 at ger.gmane.org>. I presume that it's on the list server
> even though it's not on Usenet.  Anybody know what's going on?

Something weird is going on. On google groups, this message has
a different Message-ID:
<mailman.214.1449271745.14615.python-list at python.org>

At first glance, it might look like Gmane is rewriting the
Message-IDs, but the "gmane" ID seems authentic: It appears in the
reply link in the online mailing list archive, and on the
message in my own mailbox (I use Gmane now, but didn't bother
with unsubscribing, particularly since my Email provider's
search functionality is better.)

This means the Usenet gateway (i.e. the "real" one, that goes to
comp.lang.python) is rewriting the Message-Id.  I've had the
same problem in the other direction (Reference headers for the
"mailman" Message-IDs breaking threading for me), and I'm glad
that this prompted me to investigate properly, since before
today I'd always assumed it was a Gmane problem.  Who is in
charge of the usenet gateway?