For about a week now, Newsblur has been unable to fetch this feed: http://www.kurzweilai.net/news/feed/atom
I finally went to site settings -> “Parse this rss/xml feed” and it gave me an error. Since I am a web developer, I added ?foo=1 to the URL to see if perhaps it was some sort of caching issue and then it started working!
So I have no idea how Newsblur is caching requests to feed URL’s, but I suspect there is a problem with staleness in some cases.