I cannot reproduce this, it happens somewhat randomly. I will check an RSS feed from my bookmark bar and after checking the article a (1) will remain next to the bookmark. The bookmarks are in a bookmark folder also, so they are contained in a drop down menu on my bar. Restarting safari clears the number. The website in particular for this incident (though not always same website) is www.core77.com (The RSS feed created with RSS button)
The RSS functionality is part of Safari, not WebKit. As such this bug belongs in Radar rather than Bugzilla. I'll migrate the bug over and close this one to represent that.
<rdar://problem/5657188>