为什么我的引导行没有正确布局

Question

谁能告诉我为什么这个小提琴不能正常工作？我的第三和第四逻辑行彼此重叠。它是由<div class="col-lg-8">引起的。如果我添加像<div class="col-md-12 col-lg-8">这样的col-md-12，它可以像我期望的那样工作，但是当我阅读文档时，我不需要它。如果我在第二个<div class="clear-fix"></div>

之前添加<div class="col-lg-8">，它也会有效

https://jsfiddle.net/4puugwfb/

这是代码

<div class="row">
        <div class="col-lg-8">
            <div class="fixed-height">
                double width double width double width double width double width double width double width double width double width double width double width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
<!-- Problem is this element -->
        <div class="col-lg-8">
            <div class="fixed-height">
                double width double width double width double width double width double width double width double width double width double width double width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
        <div class="col-md-6 col-lg-4">
            <div class="fixed-height">
                single width single width single width single width single width single width single width single width single width single width single width single width single width
            </div>
        </div>
    </div>