This seems to be a problem with the News Aggregator and the RSS feed generated by the Noticeboard, and not something that you've done wrong!

The duplicates are caused because it's showing one entry for each of the http and https versions of the page.

Also the feed seems to be missing some entries, even though they are obviously there in the Noticeboard.

I will look into these problems with the News Aggregator and apply a fix when it's sorted.

Thanks

Joe