[jQuery] smartposition - a scrolling detection problem.

[Brad]

I'm using some code that I found in the K2 theme for WordPress.

function smartPosition(obj) {
        // Detect if content is being scroll offscreen.
        if ( (document.documentElement.scrollTop || document.body.scrollTop)
>= jQuery(obj).offset().top) {
                jQuery('body').addClass('smartposition');
        } else {
                jQuery('body').removeClass('smartposition');
        }
}

It's supposed to add and remove the `smartposition` class when the
scrolling threshold is right.  It works perfectly in K2.

I have the style

body.smartposition #post-navigation {
  background:#FFFFFF none repeat scroll 0% 0%;
  border-bottom:1px solid #EEEEEE;
  margin:0pt;
  padding:10px 0pt;
  position:fixed;
  top:0px;
  z-index:10;
}

In my stylesheet, but the problem is that the class isn't removing!