Certainly not a major problem here, but just in case this somehow applies to handling other feeds:
I absent-mindedly copy/pasted http://rss.slashdot.org/slashdot/Classic from my previous reader, ignoring the auto-find of http://rss.slashdot.org/slashdot/classic and assuming it would be fine, but it turns out NewsBlur treats these as two separate feeds. The lower-case one has many subscribers and appears to function normally, whereas the upper-case one has just one subscriber. It says in statistics that it is updating in real-time, but it does not actually do so. The feed itself does otherwise appear to work fine though via insta-fetch.