If I understand what you've written, I disagree: it is clearly a bug and
not "understandable". As you point out, messages w/in a thread should be
in an order consistent with thread ordering. But the relative ordering of
threads themselves is - obviously - independent of threading. One should
be able to order threads however one wants (subject, date, etc.).

Suppose you start a thread called
OT: bugs in aviation.
The response to the first message comes from a "good" reader, and has
the subject
OT: bugs in aviation.
The response to that response is from a "bad" reader, and has the subject
OT: bugs in aviation.
Somebody else, with a "bad" reader, responds to the first message. His
subject line is
bugs in aviation.
Somebody with a "good" reader replies to that message. The subject is
bugs in aviation.
Someone with a good reader replies to the first message, and overrules
the subject line. His subject line is:
GPS bugs (was OT: bugs in aviation)
Someone with a good reader replies to this message. The subject is:
GPS bugs (was OT: bugs in aviation)
Someone with a very bad reader replies to the "overrule" message. The
subject line is:
bugs in aviation)
(everything in front of the colon was replaced with "re")
etc.

On Monday the first of Augtober, I read the first message in the thread.
By Tuesday, the rest of the messages have come in.
On Wednesday, I sign on again. I want to see a list of THREADS,
alphabetized by SUBJECT LINE. (I don't want to see a list of all
messages, just all threads, and the number of messages in each thread)

So, how should these messages be sorted?

Jose
--
There are two kinds of people in the world. Those that just want to
know what button to push, and those that want to know what happens when
they push the button.
for Email, make the obvious change in the address.