Some time ago, before installing Intense Debate, I had tagged links to blog posts in my RSS feed with a parameter. From the web page, the link to a post had this form:
http://stevejanke.com/archives/262257.php
In the RSS feed, the link to a post had this form:
http://stevejanke.com/archives/262257.php?utm_medium=rss
The utm_medium parameter was intended to help identify the source of clicks to Google Analytics. I never got is to work right (and in any case, I use Reinvigorate for tracking traffic) but I never bothered to remove the parameter.
I think what has been happening is that people who reach a post from an RSS feed reader were, in effect, leaving comments on a different post than the ones reached by people accessing the blog from a browser.
Oops.
So sorry about that. It was a subtle problem. I've removed the useless parameter, so going forward, everyone will see the same post (that is you, the reader, and the Intense Debate Javascripts). I've given the folks at Intense Debate a quick description of the problem and the solution so that they are aware of the pitfall some other bloggers might have fallen into without realizing it.
I don't know if the existing comment threads can be unified, and if not, I apologize to everyone who lost comments in the utm_medium hole I created.