Adam D. Barratt:
> I'm sure I'm not the only one irritated by this,
Then you should be looking at the Debian software that drives
https://lists.debian.org/ , which seriously mucks up subject processing,
and not at us poor users who are long-suffering under it. Debian
software gets References: wrong, too; which is in fact the way that one
recognizes replies. See RFC 2822 §3.6.5, which points out that Re: is
not what you think it is and describes just some of the processing that
Debian software is not doing (Try subjects with reserved punctuation
characters for even more fun!), and RFC 2822 §3.6.4, which talks about
replies and the References: header.
* https://jdebp.eu./Proposals/gnksoa-mua.html#ProperThreading
If you had directed your irritation to the bug area for the Debian
software rather than at the poor Debian software end-users, you would
have found that several bugs about some of these very things were filed
years ago, and remain unfixed to this day. As a Debian Developer, you
could probably fix these bugs.