Doug, are you having it download the entire web page or just the content of the post? On the duplicate message, are the time stamps the same or is it just that the content is the same?
I just tried it with Thunderbird and I'm not getting duplicate entries when I look at the time stamps. But, if I download the entire web page, the content in the 1:15 post is the same as the 1:25 post because it downloads the whole web page containing all the posts when you look at the post, not when it gets posted.