If the recent posts it is listing are truly the recent posts, then it will refresh with the same information until there is new information available for it.
"Recent Posts" is not a default Island. Though, it can be created using a Post Island template.
You may want to revisit your Portal Layout for the Post Island you have titled as "Recent Posts" and confirm the "Island Type" is what you're looking for... ie; New Topics vs Recent Posts.
edit: And its cache time
I dont recall that there ever was an issue with this feature not working, but if you're having trouble with this, I'd like to hear more details
