I finally figured out what the problem was…
when I modified a template of ‘single.php’ page, I moved the ‘sidebar.php’ include inside ‘content’ div and this caused the problem. As soos as I moved it outside content div and below it, the problem was solved.
drivefaroff, look at your ‘single’ and ‘comments’ files and see if you, like me, moved something around that may cause your problem…