limited threading in web interface to mailman/pipermail (confusing, when viewed alongside truer threading in Nabble)

Posted by Graham Perrin on Oct 19, 2009; 2:07pm
URL: https://support.nabble.com/limited-threading-in-web-interface-to-mailman-pipermail-confusing-when-viewed-alongside-truer-thread-tp3849241.html

At <http://lists.osafoundation.org/pipermail/chandler-users/2009-October/thread.html> 
there are two messages with the subject
[chandler-users] Use of Chandler as timeswitch (OBeMS)
(the user posted twice).

There, both messages are presented correctly.

Bug

In Nabble, both messages appeared in the midst of an unrelated topic.

In the footer of the first of the two received in my Inbox via Nabble:

> View message @ http://n2.nabble.com/Heavy-problems-on-PPC-Mac-tp3226043p3832986.html

In the footer of the second one received in my Inbox via Nabble:

> View message @ http://n2.nabble.com/Heavy-problems-on-PPC-Mac-tp3226043p3842766.html

Workaround

One of the two, I removed. The other, I moved to its proper place.

Question

Please, what could cause this bug?