title: Setting a background image in fabric.js throws an exception when clicked
body: <p>I am trying to set change the backround image for a canvas using fabric.js but running into some instability. The call to add the background works with no trouble but if I then click anywhere on the canvas it goes blank and seems to move to selection mode - although this just seems to be due to an untrapped exception.</p>
  
  <p>I cannot figure out what is causing the behavior. It works fine on this page <a href="http://fabricjs.com/customization/" rel="nofollow">http://fabricjs.com/customization/</a> but the following jsfiddle is failing <a href="http://jsfiddle.net/YH9yD/20/" rel="nofollow">http://jsfiddle.net/YH9yD/20/</a></p>
  
  <pre><code>var canvas = window._canvas = new fabric.Canvas('c');
  canvas.add(new fabric.Circle({ radius: 30, fill: '#f55', top: 100, left: 100 }));
  canvas.setBackgroundImage('http://fabricjs.com/assets/jail_cell_bars.png', canvas.renderAll.bind(canvas), {
      backgroundImageOpacity: 0.5,
      backgroundImageStretch: false
  });
  this.__canvases.push(canvas);
  </code></pre>