RSS Feed Issue with RssReader?

I started playing around with RSS feeds and the first reader I downloaded was RssReader. I found that it was inconsistant with reporting updates to my website. It can properly show the initial set if items in my feed but when I update the site it can take many hours for the RssReader to reflect the update.

I then downloaded SharpReader and found that it did not show this problem. I could add a comment or new post and hit refresh on the two readers, SharpReader shows the new comment but RssReader doesn’t.

Also, I noticed that feedvalidator.org flags a number of problems with the WordPress Feed. My feed is at:

http://www.zippoc.com/blog/?feed=rss2

The website is a WordPress 2.0.2 site and the only plugin is Spam Karma 2.

In reading the forums, there appears to be a number of folks having problems with RSS but it is unclear if they have resolved these issues.

So, is this a known problem?
If yes, is there a solution?

David