If you want to reply, but know it belongs in another topic, you can reply as linked topic and create a brand-new off-topic discussion without rousing The Dragon.
But… what if there’s already an appropriate thread? WHAT THEN!!!
<hyperventilates/>
##Here’s how I do it:
Click reply as linked topic
Copy the contents of the new message
Cancel the creation of the new topic
Go to the already-existing-topic and paste into new message
???
PROFIT
The original message in the original topic will contain a side-link to the new message in the other topic.
Because replying to the “source topic” would be off-topic, the obvious method of replying “out of band” is provided on the right.
Your example presumes we already have found the source topic as we are composing, which is hardly conducive to the fleeting thought process (mine, anyway).
Oh I see, so you discover the duplicate topic in the process of doing Reply as Linked Topic. I understand. In that case I would copy out my reply in progress into the clipboard, and paste it into a reply on that newly discovered topic.