Try to prevent the default behaviour of the click event using jQuery right from the beginning:
$optionLinks.click(function(e){
e.preventDefault();
var $this = $(this);
// don't proceed if already selected
if ( $this.hasClass('selected') ) {
return false;
}
var $optionSet = $this.parents('#filters');
$optionSets.find('.selected').removeClass('selected');
$this.addClass('selected');
//When an item is clicked, sort the items.
var selector = $(this).attr('data-filter');
$container.isotope({ filter: selector });
return false;
});