Why doesn't the SimplePie RSS script update feeds?

I’m experiencing unexpected behaviour from the SimplePie .php script.

It returns the up-to-date RSS items whenever I use a new feed source URI, sure enough, but when the feed source is updated with a new item, my WP Pages and Posts still display the original items when I refresh the browser.

I’ve cleared the IE browser Temporary Internet Files, used different browsers, and put the “no-cache” statement at the top and bottom of the pages, in case it’s a browser issue, but the result is always the same. The problem is therefore in the WP or SimplePie operations.

Even stranger is that when I create a new Post or Page with a previously used URI in the SimplePie script, it, too, displays the original items shown when I used the feed URI for the very first time, not the up-to-date ones of the feed.

It seems that WordPress itself is caching my RSS feed Pages and Posts, and is not allowing them to display the latest feed items.

Can anyone throw some light on this problem, please?