waitreally, we are sorry that we have not followed up. The Old Reader is used by hundreds of thousands of people, but there are only two of us working on it in our spare time; naturally, some things might slip through. Comparing The Old Reader to Google Reader is not really fair for this same reason - Google is a multibillion dollar corporation with thousands of top-notch engineers and millions of servers - obviously they were able to build a better product than two random guys with separate day jobs of their own. And, as you know, even though Google did not have to spend time on actually talking to their users (as we strive to do), they found the whole Reader project not worth the effort and decided to close it.
Back to the point, we found an issue earlier today that might have caused posts from several feeds to duplicate. We have pushed some adjustments that should prevent duplicates from appearing *in most cases*, and we will be properly fixing the problem during next weeks.