I just made a change to the way the RSS is built.
Previously, the only time we'd add a <link> element to an RSS item is if the headline was of type link. Otherwise we'd use the <guid> element, and its value would be the permalink to the item.
For some aggregators, apparently, this was not enough.
So now we add the <link> element if there is a permalink possible, and the information appears twice in the item.
Hopefully our feeds should work with more aggregators now.