David O'Shea has an issue where each kontrawize post shows up twice in Thunderbird, once with a kontrawize.blogs.com URL and once with a feeds.feedburner.com URL. I don't use Thunderbird (I use Opera), so I can't say anything about Thunderbird itself. However, when I started this blog it was set up with direct kontrawize.blogs.com feed URLs. Later, when I found out about FeedBurner, I set up alternative feeds URLs there, and tried to make those the default feed URLs, although I don't know for sure which feed URLs are offered to people by their feed readers when they subscribe to kontrawize.
I recommend that you use one of the FeedBurner URLs for kontrawize:
- Atom (preferred): http://feeds.feedburner.com/kontrawize-atom
- RSS1.0: http://feeds.feedburner.com/kontrawize-rss-1-0
- RSS 2.0: http://feeds.feedburner.com/kontrawize-rss-2-0
It sounds to me like David's Thunderbird has become subscribed to two separate kontrawize feeds. That kind of thing would be obvious if you did it in Opera, but I have no idea whether it could happen silently in Thunderbird. It sounds to me like what has happened, though.