If you're using Bloglines to access this site, I apologize for the somewhat sporadic RSS feed as of late. If you haven't noticed, sometimes some of the posts announce themselves as new or modified when they are neither and where I've done nothing on my end to cause their statuses to change. It's been bugging the hell out of me for a while, and earlier today I finally had some time to take a look at it.
By subscribing to my feeds in various readers I've come to think that the problem is only occurring in Bloglines and so there must be some disconnect between that service and FeedBurner. I was hoping to have the issue reproduce itself through NetNewsWire so that I could use its "Highlight differences" feature to nail down the culprit, but NNW doesn't register any changes (i.e., it's behaving correctly).
I did some digging around in the source this afternoon and have come to the conclusion that the function that WordPress uses to populate the lastBuildUpdate element of the feed is a bit wonky. It looks at the last modified date of every post (and picks the most recent), when I'm pretty sure it should limit itself to the number of items in the feed. In other words, the date should change only when one of those items currently in the feed changes; after that item is pushed off the bottom of the feed it should have no effect on it from that point forward.
So, after seeing what Movable Type's default RSS 2.0 template did (which doesn't seem quite right either), I've set the lastBuildElement equal to the pubDate element of the latest post, which requires me to run through "the loop" twice, though for the first iteration I just set query_posts() to 1 (in the second iteration I set this value to 50 so as to make sure the more frequent linked-list posts don't completely obliterate my regular feed when the regular weblog has been stagnant for a considerable amount of time).
All of this is just a long-winded way of saying "maybe it's fixed, maybe it's not." Not sure there's much else I can do about it at this point. No, it's not a pressing problem or anything, but I find it really, really annoying.
If you've any idea what may be causing this, I'd love to hear from you.