Not a huge deal, more of an annoyance. See attached image. Chrome tab and unread story show 1 unread. This has been stuck for a few weeks. I’ve tried marking all as read on most of my more common feeds but it still hangs out there. I have experienced this with Google Reader in the past and it had just cleared up if I wait long enough.
I’ve seen this from time to time as well, though it usually goes away within a day, for me.
Quite common for me - especially for particular feed folders. However in my case it won’t go away by itself - I have to manually mark a folder as read to get rid of that.