The Last Refresh filter uses the article's creation date to determine
whether the article was in the last refresh. However, Vienna now shows
articles that have been updated after they were created. The Last Refresh
filter leaves out updated articles that were in the last refresh.
This problem was first reported at http://forums.cocoaforge.com/
viewtopic.php?t=8926. I also discussed the problem and what to do
about it at http://forums.cocoaforge.com/viewtopic.php?t=8927.