pgarchives: issue (?) when responding to a message on another list

I've fixed the issue with primary keys listed in another thread [1] and now encounter a strange behaviour when testing: responding to a message on a different list than the original recipient list saves this message in both lists' archives (it is saved in the database once, but appears on both lists). I'm now wondering if this is expected behaviour or a problem in my fix or install.
Given that messages belong to threads (and not lists), which can belong to several lists, I guess this is the intended behaviour.

This use case happens for instance when a user responds to a message posted in an *-announce list to a more general list. In such case, it is inappropriate to archive the message in the more restricted *-announce list.
I've looked for an example in postgresql archives to see if this happens in the deployment for postgresql but haven't managed to find one as it's pretty rare.

[1]: https://www.postgresql.org/message-id/CABUevExzjRo-=9Hg4CDdnGHuQB1L6uAwekni0mz-1CECaMcGZA@mail.gmail.com
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Célestin Matte