I've many RSS feeds in my bookmarks collection.
Safari appends the number of new/unread items to the RSS title. It is really convenient, as I have many RSS feeds I am interested in (and it makes a huge collection), so I only need to check every day which one get updated to click on it. No need to check them one by one. That is what RSS is for, AFAIK (a main feature at least?)
But some of them never get updated. For some of them I need to double click on it to discover it has recent news. Now I've pointed out which rss feeds have that issue (xkcd rss feeds, Linux weekly news, and others), I check them out regularly to get sure I miss nothing (xkcd being the most important one of course)
Did you ever experiment that issue in Safari and how to get rid of it? Could it be the website that does not work properly ?