css – 为什么webkit过滤器上的堆叠顺序更改悬停？

在应用webkit过滤器时,我注意到堆叠顺序存在一个奇怪的问题.为什么当我将鼠标悬停在图像上时,堆叠顺序会发生变化？

我宁愿不必使用z-indexing来解决这个问题,因为它打破了其他网站元素.

这是我的JSFiddle
http://jsfiddle.net/r13ycy1p/

请原谅荷马,我只需要一张图片.

编辑：如何反转效果以阻止绝对位置div被隐藏？

这是我的HTML

<ul>
<li>
    <a href="#">
        <div class="slide-content">
            <div class="slide-title">
                <h1>hello world</h1>
            </div>
            <div class="slide-desc">
                <p>a description about something</p>
            </div>
        </div>
        <img src="http://img4.wikia.nocookie.net/__cb20130920142351/simpsons/images/e/e9/Pic_1187696292_8.jpg"/>

    </a>
</li>
</ul>

CSS

li {
list-style:none;    
}

.slide-content {
position:absolute;
color:red;
top:50px;
}

li a:hover img{
-webkit-filter: grayscale(100%); /* For Webkit browsers */
}

解决方法

这是因为非none以外的值建立了 stacking context.这在 spec中记录(当前处于工作草案状态)：

07002

This specification defines a set of CSS properties that affect the
visual rendering of elements to which those properties are applied;
these effects are applied after elements have been sized and
positioned according to the Visual formatting model from [CSS21]. Some
values of these properties result in the creation of a containing
block,and/or the creation of a stacking context.

该规范还指出：

07003

A computed value of other than none results in the creation of a stacking context [CSS21] the same way that CSS opacity does.