I was able to contact Open RSS about this. It appears that Newsblur’s feed finder is making a lot of requests to paths on the openrss.org server that are not valid and doing it in rapid succession. So the app gets blocked. Attached request logs. I’m guessing Newsblur is trying to find RSS feeds at paths that don’t exist?
They also are saying that they have logs that show Newsblur making over 20 requests within a second. No screenshot was provided, but making that many requests at the same time isn’t good.