这很可能是因为动画/淡入淡出切换代码在另一次点击发生之前没有完成。
你应该阻止你的点击功能的处理，直到动画完成。为了实现这一点，我会做以下事情：
添加一个全局布尔变量来跟踪动画的状态，比如.. var animating = false;
将所有的click函数 Package 在一个if块中，这样它们就不会运行if
animating为true。在块if( ! animating ) { animating = true; ... }中也将animating设置为true
最后一步是在fadeToggle的完整回调中将animating设置为false：$('#' + thisItem).fadeToggle(500, "linear", function() { animating = false; });

您需要将.stop()和.stopPropagation()添加到所有动画函数中，以防止它们彼此“冲突”：JSFiddle
另外，不要忘记你的CSS中的结束括号}，它会把一切都搞砸。

// Testimonials
var thisItem = 1, nextItem = 0, range = 0
//for each content item, set an id, and hide.
$('.testimonial-item').each(function () {
  nextItem++;
  $(this).attr('id', nextItem).stop().hide();
});
//range contains how many content items exist
range = nextItem, nextItem = 2, prevItem = range;
//display the first content item
thisHeight = $('#' + thisItem).stop().height();
$('#' + thisItem).stop().show();
$('.testimonials').css('height', thisHeight);
//hide old content item, show next item, resize content container
$('.testimonial-control.next').click(function (e) {
    e.stopPropagation();
  prevItem = thisItem;
  //get height of next content item to resize container
  thisHeight = $('#' + nextItem).stop().height();
  //resize content container
  $('.testimonials').stop().animate({
    height: (thisHeight + 'px')
  }, 250, 'swing');
  //hide old content item
  $('#' + thisItem).stop().fadeToggle(500, "linear");
  //show next content item
  $('#' + nextItem).stop().fadeToggle(500, "linear");
  //set old content item to current item
  thisItem = nextItem;
  //loop to first item if range reached
  if (thisItem >= range) {
    nextItem = 1; prevItem = range - 1;
  } else {
    nextItem++; prevItem = thisItem - 1;
  }
});
//end next click function
//hide current content item, resize content container, show previous item 
$('.testimonial-control.prev').click(function (e) {
    e.stopPropagation();
  //If we have reached the end range, the next item will be item #1
  if (nextItem == 1) {//so set the current item to the last
    thisItem = range;
  } else thisItem = nextItem - 1;
  //get height of next content item to resize container
  thisHeight = $('#' + prevItem).stop().height();
  //resize content container
  $('.testimonials').stop().animate({
    height: (thisHeight + 'px')
  }, 250, 'swing');
  //hide old content item
  $('#' + thisItem).stop().fadeToggle(500, "linear");
  //show next content item
  $('#' + prevItem).stop().fadeToggle(500, "linear");
  //set next content item to current item
  nextItem = thisItem;
  if (prevItem >= range) {//if at end of items
    nextItem = 1;//first
    prevItem = range - 1;
    thisItem = range;
  } else if (prevItem <= 1) {//if at start of items
    prevItem = range;
    thisItem = 1;
    nextItem = 2;
  } else {//if in the middle of items
    prevItem--;
    thisItem--;
  }
});
//end prev click function