Mail.app - any way to split mail threads?

[malone]

I love setting my mail view to "Organize by Thread". They make tracking down emails easier, especially for conversations that have been going on for weeks or months.

But sometimes Mail.app messes it up and lumps some emails together that are completely unrelated. How do I separate/split them?

 

[Lone Deranger]

I have noticed this phenomenon of incorrectly sorted threads in 'Mail' as well.
Being subscribed to a mailinglist, I've created a separate mailbox for it and have set it to 'Organize by thread". But it's more miss than hit.
What's particularly annoying about it is when the threads are collapsed down to a single line, you only get to see one of the "merged" subject titles. This makes trying to find the threads you're looking for somewhat inconvenient (not always wanting to resort to a spotlight search in 'Mail').
I'm suspecting this is a bug and am considering reporting it to Apple.