I answered this 10 minutes ago in your other issue:

This is an old issue caused by Mailman rewriting message-IDs. It is a long-standing anti-feature that causes breakages in software like this. On the forum, it happens when a mailing-list user replies to another mailing-list user.

#98 (comment)

• is there any workaround or it's really hard to fix? couldn't we merge issues by title which only differ by leading Re:* ?

• who can I (as a user) not cause it? reply only to mailing list but not "reply all" ?

is there any workaround or it's really hard to fix?

A workaround is possible:

• Subscribe to both NNTP and mailing list
• Keep track of two message-IDs per message
• When a message is received on both, try to match up their message IDs

couldn't we merge issues by title which only differ by leading Re:* ?

That would be error-prone, there are many threads with the same title.

who can I (as a user) not cause it?

Don't use the mailing lists to post - use forum.dlang.org or NNTP instead.

I found this:
https://www.mail-archive.com/[email protected]/msg63313.html

unfortunatily mailman is rewriting the Message-Id of
> > the injected emails.
> 
> 
> What Mailman version is this? This should not happen unless General
> Options -> anonymous_list is Yes or the new in 2.1.16 General Options ->
> from_is_list setting is Wrap Message.
> 

Hei Presto,

Changing the setting of anonymous_list to no has resulted in the correct
Message-Id.

Thanks for the fast and correct response.

@timotheecour Sounds like that might be relevant for our little problem here. Can we at least try this out to see if it works? ping @CyberShadow

Well, we would need to ask Brad to change the setting.

Does anonymous_list have any side effects other than disabling the mangling of message IDs?

Honestly, I have no idea. But perhaps @brad-anderson would know?

That's the wrong Brad, you want @braddr :)

Haha, thanks!