I figured someone else would have reported this but Search within a feed is broken. You can easily test this by searching for gibberish or even a real word that you know is unlikely to be in a feed. Basically, nothing gets filtered. You still see all the items in the feed.
On a related note, it would be very helpful to search only titles. And also for the search field to support searching for phrases when placed in quotes — for example “Microsoft Word” It seems like there should be some open source project at this point that would modernize NewsBlur search.