mybearworld

The topics themselves aren't considered new or old. The “(New posts)” thing appears when someone has posted something on that topic and you haven't seein it yet.
When a topic has been up for 10 minutes, but you haven't seen it yet, it'll say “(New posts)”.
When a topic has been up for 1 minute, but you clicked on it and there's been no new posts since, it'll not say “(New posts)”.