Dave,
I purposely made sure I didn't double click. When I saw that there was a response to the thread I clicked one time on the thread, then when it came up on the right it said Jump to end. I clicked one time on that. It doesn't happen on every thread.
I did have to mark this one as "Unread" a little bit ago, and come back to it so I expected to see the Jump to end then.
It's not that big a deal, I was just curious, especially as sometimes I get pretty far behind on some threads, and instead of taking me to first unread it was giving me the jump to end then I had to scroll back up to figure out where I had left off.
You have better/more important things to do than worry about this.