This is interesting. So, I forgot to remove old, already sent patches from the work dir (usually I remove whole thing but didn't do that now). So I had 2 patch series in the same dir, one old already sent and applied, and one new. And did git send-email series/* - which obviously included both.
But the fun part is the References: headers and hence threading. I used git format-patch --cover-letter $since-commit. Git created the cover letter with Message-Id 20230823055155.1917375-1-...@tls.msk.ru. And used this Id in References: header of the *first* patch. But in all subsequent patches 2..24, it used *another* ID in the References: header, the one taken from the *old* cover letter, which it replaced when generating the new cover. Obviously I did not edit the messages, did not specify anything more fancy besides --cover-letter, - the only issue was that I had another 4-file patch series in the same dir. This smells like an.. interesting bug in git.. :) /mjt
