Threading a Needle

We need a brief guide to posting. Perhaps there is one and I've missed it. I'd like to see something done to encourage people to reply in the appropriate place using the buttons provided.

Look:

This is clearly a response to this, but the author has chosen to create a new thread.

While this is clearly a response to this (you can tell because it's posted under the existing thread), this is also probably a response to same, but in its own thread.

Maybe I'm the one getting it wrong?