It's a per forum option: "Include threads from this forum when users click "New Posts"". It should exist in 1.3. That (or the thread already being considered read) are the only reasons (out of the box) that would cause things to not be shown in new posts.
Based on this, it sounds like a misunderstanding of what's a new post. Posts you have read (or more correctly, have viewed) are not new; a post you made yourself is, by definition, read so it doesn't show up. He can click the "recent posts" link from the new posts page if he wants to see already viewed stuff as well.