mailing list errors not being sent to list owner

["Guy Middleton (foo)" <gamiddle@watdragon.uwaterloo.ca>]

I have a mailing list which generates an error, but the error is sent
to the message sender, rather than the owner of the list data file.

This is puzzling, since the router does know the correct owner of the list:

% router -i
ZMailer router (2.2 #2: Fri Oct 23 12:02:19 EDT 1992)
  gamiddle@taipan:/usr/source3/TEMP-CACHE/zmailer/src/router
Copyright 1992 Rayan S. Zachariassen

z$ router bloop-owner
<gamiddle.interactive@taipan.uwaterloo.ca>: address: bloop-owner
(((local - gamiddle default_attributes)))
z$ ^D
%

I'm sure I have something misconfigured somewhere.  Does anybody know what?
Here is the error message:

  From taipan.uwaterloo.ca!mailer-daemon Wed Oct 28 13:51:09 1992
  To: <gamiddle@watdragon.uwaterloo.ca>
  From: The Post Office <postmaster@taipan.uwaterloo.ca>
  Subject: Delivery problems with your mail
  Date: Wed, 28 Oct 1992 13:50:40 -0500
  
  A copy of your message is being returned to you due to difficulties
  encountered while attempting to deliver your mail.
  
  The following errors occurred during message delivery processing:
  
  
  <smtp math.uwaterloo.ca zowie@math.uwaterloo.ca 192>: 550 <zowie@math.uwaterloo.ca>... User unknown
  
  ----------  Original Message  ----------
  external
  rcvdfrom watdragon.uwaterloo.ca ([129.97.140.24])
  with SMTP
  from <gamiddle@watdragon.uwaterloo.ca>
  to <bloop@taipan.uwaterloo.ca>
  Received: by watdragon.uwaterloo.ca id <168760-3>; Wed, 28 Oct 1992 13:50:06 -0500
  From: "Guy Middleton (foo)" <gamiddle@watdragon.uwaterloo.ca>
  To: bloop@taipan.uwaterloo.ca
  Subject: asdf
  Message-Id: <92Oct28.135006est.168760-3@watdragon.uwaterloo.ca>
  Date: Wed, 28 Oct 1992 13:50:03 -0500
  
  asdf