I was trying to move some of the messages of one topic into another one as they had gone off-topic.
Part-1: There is a bug somewhere in the merge process that causes merged messages to remember their previous (pre-merge topic) subject and use that to pre-fill the subject field when replying online.
To replicate this: (happened in an unmoderated group)
1. Split let's say half of the messages in a topic (eg. TopicA) into another one, let's say TempTopic
2. Merge the new TempTopic into another one, let's say TopicB
3. Go now into TopicB. If you online-reply to any of the original already-existing TopicB messages, the subject gets correctly pre-filled with Re:TopicB.
4. But if you online-reply to any of the merged messages from the old TempTopic, the subject gets incorrectly pre-filled with Re:TempTopic instead of the correct Re:TopicB. Then for this case:
4a - If one doesn't notice this erroneous pre-filled subject and leaves it as such, the online reply does correctly thread under TopicB (and the email does go out with Re:TopicB). But, any subsequent online replies to this online reply still persist in pre-filling the subject with the incorrect Re:TempTopic, unless the cycle is broken by correcting the reply subject, and going forward. The previous merged messages and uncorrected-subject replies still keep remembering the incorrect subject if one online-replies to them later on.
Namely, one used email to reply to one of the original TopicA messages which by now had gotten moved (through the merge) to TopicB. Their emailed reply of course still has TopicA in the subject. You'd think it would thread under TopicA due to having the same subject and stop there, but maybe because the reply message's InReplyTo value is referencing a message which now belongs to a different topic and therefore subjects no longer match between those two, something didn't work right in threading so it just created a brand new topic, with the same exact TopicA title.
So there's a bit of a mess going on and I put these topics in moderation so I can manually adjust the subjects as they come in, or at least that's the idea. This happened yesterday and so far I haven't gotten any new replies to either TopicA, TopicB, or cloned TopicA, so I don't know yet if changing the subject will help thread correctly into them going forward. I was going to merge the cloned TopicA back into the original TopicA but I left it there for now for your examination if needed.Cheers,