Ignoring events on a higher positioned object

HTML

<script src="https://rawgithub.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas id="c" width="500" height="500" style="border:1px solid #ccc"></canvas>

JavaScript

var canvas = new fabric.Canvas('c');

var rect1 = new fabric.Rect({
    left: 200,
    top: 200,
    width: 200,
    height: 200,
    fill: 'rgba(255,0,0,0.5)',
    selectable: false
});

var rect2 = new fabric.Rect({
    left: 200,
    top: 200,
    width: 100,
    height: 100,
    fill: 'gray'
});

canvas.add(rect2, rect1);