ios 输入框 聚焦 header标签 移动

ios ，焦点在输入框上的时候，拖动页面，整个<header></header>标签里的内容出现移动，是怎么回事？

<header class="mui-bar mui-bar-nav">
<a class="mui-action-back mui-icon mui-icon-left-nav mui-pull-left"></a>
<h1 class="mui-title">产业工人平台</h1>
</header>
<div class="mui-content">
<div class="mui-fullscreen">
<form class="mui-input-group">
<div class="mui-input-row">
<label>服务地址</label>
<input id='txt_domain' type="text" class="mui-input-clear mui-input" placeholder="请输入服务地址，如：qzsm"
style="ime-mode: disabled" value="qzsm"/>
</div>
</form>
<div class="mui-content-padded">
<button id='btn_server_confirm' class="mui-btn mui-btn-block mui-btn-green">确认</button>
</div>
</div>
</div>