I've searched all over the web for solutions to this but can't find one, so
this forum is my last hope.

This is NOT the problem of feeds not updating. My feeds are updating fine
and indicating when new items are found. I use a 1 hour default update, and
after an hour some feeds are indicated in bold and have the new content.

What is happening is that for some feeds, IE is sometimes not including the
latest items in the feed. But if I look at the feed with Firefox or send the
feed to feedvalidator, they both show the latest items that IE is not showing.

I am not sure what types of feeds this happens for, but it does for all 4 of
my feeds that are on 2 of my sites. Three of those feeds are produced by
WordPress and one is by bbPress. I have compared the xml in the feed with
other feeds that do not have this problem, and I don't see anything that
might be causing this.

I have attempted just about everything, including deleting IE's feed folder
(it's cache) and changing some of the attributes within the feeds themselves,
and even clearing the WordPress feed cache, but the problem persists.
Because the items are truly in the feed and Firefox and feedvalidator can
read them, I presume it must be a problem with IE.

This problem has been happening for at least the last 6 months in IE 7. I
decided to try the IE 8 release candidate today and hoped this problem would
be fixed. But it happens in IE 8 as well.

Has anyone else notice this happening to them?

Does anyone have any ideas of what may be happening, or any ideas of what I
might try to fix this? Any help would be very much appreciated.

With much work, I discovered the problem wasn't IE's fault. It was WordPress.
The problem then was a stale “Last-Modified:” header in the HTTP response to
the link to the comments feed.

I have now fixed this in WordPress and everything works fine. If you are
interested, see my blog entry on this problem:
http://www.beholdgenealogy.com/blog/?p=667