[Users] "Thread using subject in addition to standard headers" not working?

[Thomas Leitner]

On 2021-01-11 07:36 -0000 Paul wrote:
> > Am I missing something here in how the option works?
>
> Is the parent message in your folder? Threading needs the parent.

Yes, all the messages are in the same folder. However, how would Claws
determine the "parent message" if threaded by subject? Because the
In-Reply-To and References headers of all those messages are the same
in my case.

-- Thomas