Hi Sam,
The reason for the choice of unlisted was merely temporary. It was so that I could copy and paste the relevant chunks of text from the original posters topic into a new topic, change ownership of it to them, then move the relevant posts from the original topic to this one - then - editing the original one so that it made sense again and was tidy. At the end of the process the topic was set to listed again. The use of unlisted was merely to keep all of the to-and-fro from the public eye whilst it was happening.
I like all of the bullet point items you raise, especially the third one, the warning etc.
p.s. thanks for the correction, I wasn’t trying to assume it was a bug per-se, I just couldn’t think why I would be able to move posts to an unlisted topic via ID but not title. 