Ever wonder? The "New" Icon only shows up on posts that you have not viewed. When you post a new piece, it automatically counts as a view. Once someone comments/reviews it, you'll notice the "New" tag will be there again until you've read the thread.
In other words, if you've not looked at the thread since the time it was posted or after someone else has commented/reviewed it, you'll see the "New"! When you read the thread, it'll go away, but still shows up "New" for those who haven't.