Plotly stacked line hover

Hover over filled in areas - no hover tooltip appears.

HTML

<html>
  <head>
  </head>
  <body>
    <div id="test"></div>
    <script src="https://cdn.plot.ly/plotly-latest.js"></script>
  </body>
</html>

JavaScript

Plotly.newPlot('test', [
	{x: [1,2,3], y: [2,1,4], stackgroup: 'one', hoveron: 'fills', name: "a"},
	{x: [1,2,3], y: [1,1,2], stackgroup: 'one', hoveron: 'fills', name: "b"},
]);