I have used Newsblur since shortly after Google Reader shut down. For as long as I can remember, from desktops, laptops, from Windows to Linux, there has been a bug mistakenly marking articles as read that have not been read.
How to reproduce the bug:
Step 1: Go to a feed in feed view, select an item to view.
Step 2: Hit J to advance to next item.
Step 3: Hit J one or two more times to advance to next item.
Step 4: Look at items below your selected item, and note that there are now new items marked as read in feed, even though you have not opened them. Several items below your current item will now be marked as read that had not been marked as read when you started at step 1.
I have known about this for years. I believe for as long as I have used Newsblur. I posted a thread about this a year and a half ago which was ignored. For this post, I tested it with The Verge RSS feed, although it works with numerous RSS feeds.
Given previous experience, my expectation is that this bug, practically as old as Newsblur itself, will again be ignored. So at this point I longer expect that it will actually be fixed, and I guess I just want it on the record in case newsblur ever does a self-assessment of how responsive they are to concerns of longtime users and are looking for ways to improve.