Last item in TOC keeps getting set to active

[legos]

I'm not sure what's going on but the last item in my TOC keeps being set as the active one when I scroll to the top of the page. Any thoughts?

[scinart]

with following hackings, I managed to let it working, at least it seems to work on my github.io
I'm not quite familiar with jQuery though.

  for (var i = 0, c = headingOffsets.length; i < c; i++) {
    if (headingOffsets[i] >= top) {
      $('li', self).removeClass(activeClassName);
<<<<
      highlighted = $('li:eq('+(i-1)+')', self).addClass(activeClassName);
====
      highlighted = $('li:eq('+((i-1)<0?0:i-1)+')', self).addClass(activeClassName);
>>>>
      opts.onHighlight(highlighted);
      break;
    }
  }
<<<<
====
  // added by scinart.
  if (i == headingOffsets.length)
  {
    $('li', self).removeClass(activeClassName);
    highlighted = $('li:eq('+(i-1)+')', self).addClass(activeClassName);
    opts.onHighlight(highlighted);
  }
>>>>