Here's what's happening. when you are reading posts and you get to the bottom, there is a "next" button.
If there's some more posts in the thread, it will show them.
If there are no more posts in that thread, the "next" button will send you to another thread but not at the beginning of the other thread. It's always down several posts.
It can sometimes seem like changing horses in the middle of the stream.
If any of this makes sense, I hope it can be fixed.
That's what caused me to think threads were being combined. the second thread, if it had similar posts, was confusing.
Or, I'm losing my mind.