iOS overflow scrolling z-index issue

Tests on issue described here https://github.com/scottjehl/Device-Bugs/issues/14

by Aides

HTML

<body>
  <div class="splitscreen">
    <div class="list">
      <header>
        <h1>List</h1>
       </header>
       <ul>
         <li>Item 1</li>
         <li>Item 2</li>
         <li>Item 3</li>
         <li>Item 4</li>
         <li>Item 5</li>
         <li>Item 6</li>
       </ul>    
      </div><!-- /list -->
     <div class="detail">
       <header>
         <h1>Detail View</h1>
       </header>
       <div class="content">
         <h2>Item 1</h2>
         <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
         <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
         <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
         <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad...

CSS

header {
    background-color: #fff;
    border-bottom: solid 1px #999;
    margin-bottom: 10px;
    position: fixed;
    z-index: 2;
}
h1, h2, p {
    margin-bottom: 10px;
}
h1 {
    font-size: 1.5em;
}
.splitscreen {
    display: -webkit-box;
    -webkit-box-orient: horizontal;
    position: relative;
    width: 100%;
}
.list, .detail {
    padding: 20px;
}
.list {
    border-bottom: 1px solid #666;
    border-right: 1px solid #666;     
    width: 20%;
}
.list header {
    width: 20%;
}
.detail {
    -webkit-box-flex: 1;
    position: relative;
}
.detail header {
    width: 72%;           
}
.list ul, .content {
    padding-top: 70px;
}
.content {
    -webkit-overflow-scrolling: touch;
    height: 600px;
    position: absolute;
    overflow-y: scroll;
}    
.lightbox {
    background: rgba(0,0,0,.3);
    height: 600px;
    left: 0;
    position: absolute;
    right: 0;
    top: 0;
    z-index: 3;
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
}
.modal-content {
    background: #fff;
    margin: 15% auto;
    padding: 20px;
    position: relative;
    width: 50%;
    z-index: 4;
}