jsplumb无法连接嵌套的div元素

Question

我正在使用jsplumb 1.7.10和bootstrap 3.3.5。我无法连接嵌套div上的按钮。我也用过容器。

这是fiddle。尝试将source0连接到目标。

如何连接theese按钮？

JS代码：

<div class="portlet light bordered">
    <div class="portlet-body">
        <div class="row" id="container">
            <div class="col-md-12">
                <div class="col-md-6">
                    <div class="portlet box blue">
                        <div class="portlet-title">
                            <div class="caption"> <i class="fa fa-gift"></i>Keys1</div>
                        </div>
                        <div class="portlet-body text-center">
                            <div class="btn-group-vertical">
                                <button id="src_0" class="btn blue" type="button" style="width:200px">src0</button>
                            </div>
                        </div>
                    </div>
                </div>
                <div class="col-md-6">
                    <div class="portlet box green-sharp">
                        <div class="portlet-title">
                            <div class="caption"> <i class="fa fa-gift"></i>Keys2</div>
                        </div>
                        <div class="portlet-body text-center">
                            <div class="btn-group-vertical">
                                <button id="tgt_0" class="btn blue" type="button" style="width:200px">tgt0</button>
                                <button id="tgt_1" class="btn blue" type="button" style="width:200px">tgt1</button>
                                <button id="tgt_2" class="btn blue" type="button" style="width:200px">tgt2</button>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

HTML：

rand()