I think it’s too early to point the finger at anyone (or anything). If you’d like help with this, I’d suggest you create a test case on jsfiddle.net or jsbin.com. And please specify the version of IE in which you’re seeing the problem.

Class each button, be it open or close/ Leave the open/toggle as it is, but add another function that will close the ‘parent’ div of where the close button is located, which was originally the ‘next’ element that the first function opened. See the code below for a better idea of what I mean. It may not be the best solution but it works. Hope it helps someone.

HTML:

  slide it
slide itAnimate this element's margin-left style property

Jquery:

$(document).ready(function() {

  $('.slidemarginleft button.open').click(function() {
    var $marginLefty = $(this).next();
    $marginLefty.animate({
      marginLeft: parseInt($marginLefty.css('marginLeft'),10) == 0 ?
      $marginLefty.outerWidth() :
      0
    });
  });

    $('.inner button.close').click(function() {
    var $marginLefty = $(this).parent();
    $marginLefty.animate({
      marginLeft: parseInt($marginLefty.css('marginLeft'),10) == 0 ?
      $marginLefty.outerWidth() :
      0
    });
  });

});

anyone else having problems with it right to left appearing on load inspect this demo
http://test.learningjquery.com/moreslide.html