BackstopJS: Casper JS click fails screencapture

Hello,

My casper script is a simple click and it causes the screen capture to mess up.

Here is my JSON file (you can test it yourself)

{
  "viewports": [
    {
      "name": "tablet_h",
      "width": 1024,
      "height": 768
    }
  ],
  "scenarios": [
    {
      "label": "Tous les boutons",
      "url": "http://s.codepen.io/stephendesjardins/debug/BLLPmK",
      "referenceUrl": "http://s.codepen.io/stephendesjardins/debug/BLLPmK",
      "selectors": [
        "#boutons"
      ],
      "misMatchThreshold" : 1
    },
    {
      "label": "Bouton divisé",
      "url": "http://s.codepen.io/stephendesjardins/debug/BLLPmK",
      "referenceUrl": "http://s.codepen.io/stephendesjardins/debug/BLLPmK",
      "selectors": [
        ".dropdown-divise"
      ],
      "misMatchThreshold" : 1,
      "onReadyScript": "button-interaction.js"
    }
  ],
  "paths": {
    "bitmaps_reference": "../../backstop_data/bitmaps_reference",
    "bitmaps_test": "../../backstop_data/bitmaps_test",
    "compare_data": "../../backstop_data/bitmaps_test/compare.json",
    "casper_scripts": "../../backstop_data/casper_scripts"
  },
  "engine": "phantomjs",
  "report": ["browser", "CLI"],
  "debug": false,
  "port": 3001
}

Casper script :

module.exports = function(casper, scenario, vp) {
    casper.click('.dropdown-divise .dropdown-toggle');
    casper.wait(250);
}

Codepen I am using for my test in the json file : http://codepen.io/stephendesjardins/pen/BLLPmK?editors=1000 http://s.codepen.io/stephendesjardins/debug/BLLPmK

Thanks