[Evolution] threading didn't work in reply-to-all

[Iain Buchanan <iaindb netspace net au>]

I just replied to a message on an internal mailing list that I'm
subscribed to at work.  I used the reply to all button, then I deleted
the OP's email from "to" (because he's on the list as well), and then
moved the list email from "cc" to "to".

Because I get my own posts from this list, I would expect it would be
threaded under the OP's email in my inbox, but instead it appeared by
itself.

I had a look at the "email source".  The OP contains
Message-ID: <42C326C9 7010307 pcorp com au>

and my reply contains
In-Reply-To: <42C326C9 7010307 pcorp com au>
 References: <42C326C9 7010307 pcorp com au>
Message-Id: <1120175637 26899 31 camel orpheus>

so obviously evolution understands both the OP's style of threading and
its own (good :)

so why didn't it "thread"?  I have the correct view, because other
messages in my inbox are "threaded", ie. indented one below the other,
but this one isn't.

Any help would be greatly appreciated,
TIA,
-- 
Iain Buchanan <iaindb netspace net au>

Parkinson's Law:  Work expands to fill the time alloted it.