首页下拉刷新第一次加载拉不动，第二次加载可以正常下拉

文件结构：
index.html
list.html

index.html加载list.html作为子页面
然后list.html做上拉下拉，真机运行，子页面向下拉拉不动，向上正常

然后随便修改下list.html 保存后，自动同步真机运行，发现下拉可以用了，第一次加载不能用
这是为什么吗，是因为webview加载问题吗？

index.html

<header class="mui-bar mui-bar-nav navbar">  
            <a id="menu-btn" class="index_nav mui-pull-left" href="javascript:;">筛选</a>  
            <a id="info" href="javascript:;" class="index_nav mui-pull-right" href="javascript:;">提问</a>  
            <h1 class="mui-title">全部</h1>  
        </header>  
        <div class="mui-content">  

        </div>  
<script>  
            var menu = null,list=null,main=null;  
            var showMenu = false;  
            mui.init({  
                swipeBack: false,  
                statusBarBackground:'#f7f7f7',  
                subpages: [{  
                    id: 'list',  
                    url: 'list.html',  
                    styles: {  
                        top: '48px',  
                        bottom: 0,  
                        bounce: 'vertical'  
                    }  
                }]  
            });  
</script>  

//list.html 代码  
<!--下拉刷新容器-->  
        <div id="pullrefresh" class="mui-content mui-scroll-wrapper">  
            <div class="mui-scroll">  
                <!--数据列表-->  
                <ul class="mui-table-view mui-table-view-chevron">  

                </ul>  
            </div>  
        </div>  

<script>  
            mui.init({  
                swipeBack: false,  
                pullRefresh: {  
                    container: '#pullrefresh',  
                    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('#pullrefresh').pullRefresh().endPulldownToRefresh(); //refresh completed  
                }, 1500);  
            }  
            var count = 0;  
            /**  
             * 上拉加载具体业务实现  
             */  
            function pullupRefresh() {  
                setTimeout(function() {  
                    mui('#pullrefresh').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);  
            }  
            if (mui.os.plus) {  
                mui.plusReady(function() {  
                    setTimeout(function() {  
                        mui('#pullrefresh').pullRefresh().pullupLoading();  
                    }, 1000);  

                });  
            } else {  
                mui.ready(function() {  
                    mui('#pullrefresh').pullRefresh().pullupLoading();  
                });  
            }  
        </script>