It's started adding the 1 New Post thing again in the User CP section. Fortunately "Mark Forum As Read" clears it out.

I've seen it alone (when there aren't any new posts) as well as added to real new posts (for example... when there are actually 2 new posts, it shows as being 3 new posts). It seems to come and go for me, so I'm not sure if it's just hiccuping when changes are being made to the forum or not.

Hope this helps.