Try to not click on the button labeled “New post”. Despite the label. it does not actually make a new post in the same thread - it starts a totally new thread, divorced from the thread you are trying to follow up on. The button ought to not have been there. Instead, to follow up on a thread, click on “reply” on one of the posts.
Here is the thread you no doubt was trying to follow up on: http://cs.trains.com/mrr/f/88/t/209532.aspx
Smile,
Stein