I discovered that when you click on "New Posts" you don't actually see all the new posts, only new posts that you haven't viewed yet. If you look to the right, at the top of the list is a link for "Recent Posts", that will show all the latest posts. That should be what you check if you want to see all the most recent posts. This is a reason why you might not see that new post you just made in the new posts list... because you've already seen it. It will reappear as soon as someone else replies as there is now a "new" post you haven't seen. Weird, I know.
Can you put a link somewhere more obvious, what used to be active topics, now recent posts is where I, and I am guessing most people go first to navigate