使用mui下拉刷新问题

在页面初始化时，上拉时可以调用pullupRefresh。下拉时不调用 pulldownRefresh这个方法，什么原因？？
mui.init({
swipeBack: false,
pullRefresh: {
container: '#pullrefresh1',
down: {
callback: pulldownRefresh
},
up: {
contentrefresh: '正在加载...',
callback: pullupRefresh
}
}
});

/**

• 下拉刷新具体业务实现
  */
  function pulldownRefresh() {
  setTimeout(function() {
  var table = document.body.querySelector('.mui-table-view');
  var cells = document.body.querySelectorAll('.mui-table-view-cell');
  for (var i = cells.length, len = i + 3; i < len; i++) {
  var li = document.createElement('li');
  li.className = 'mui-table-view-cell';
  li.innerHTML = '<a class="mui-navigate-right">Item ' + (i + 1) + '</a>';
  //下拉刷新，新纪录插到最前面；
  table.insertBefore(li, table.firstChild);
  }
  mui('#pullrefresh1').pullRefresh().endPulldownToRefresh(); //refresh completed
  }, 1500);
  }
  var count = 0;
  /**
• 上拉加载具体业务实现
  */
  function pullupRefresh() {
  setTimeout(function() {
  mui('#pullrefresh1').pullRefresh().endPullupToRefresh((++count > 2)); //参数为true代表没有更多数据了。
  var table = document.body.querySelector('.mui-table-view');
  var cells = document.body.querySelectorAll('.mui-table-view-cell');
  for (var i = cells.length, len = i + 20; i < len; i++) {
  var li = document.createElement('li');
  li.className = 'mui-table-view-cell';
  li.innerHTML = '<a class="mui-navigate-right">Item ' + (i + 1) + '</a>';
  table.appendChild(li);
  }
  }, 1500);
  }