How to correctly display stacked data using nvd3.js multiBarChart

I am using nvd3.js to create a multibyte chart. Here is my code:

$(function() {

    $.get('/charts/objects_created/')
        .done(function(resp) {
            init_graphs(resp);
        });

    function init_graphs(data) {
        nv.addGraph(function() {
            var chart = nv.models.multiBarChart();
            chart.xAxis.tickFormat(function(d) {
                return d3.time.format('%x')(new Date(d));
            });

            chart.yAxis.tickFormat(d3.format(',d'));

            d3.select('.chart#recent_activity svg')
                .datum(data)
                .transition().duration(500).call(chart);

            nv.utils.windowResize(chart.update);

            return chart;
        });
    }
});

and here is my data:

[
   {
      "values":[
         {
            "y":3,
            "x":"04/05/2013"
         },
         {
            "y":1,
            "x":"04/11/2013"
         },
         {
            "y":3,
            "x":"04/12/2013"
         }
      ],
      "key":"Apples"
   },
   {
      "values":[
         {
            "y":3,
            "x":"04/05/2013"
         },
         {
            "y":1,
            "x":"04/12/2013"
         },
         {
            "y":0,
            "x":"04/11/2013"
         }
      ],
      "key":"Oranges"
   }
]

It looks wonderfully grouped:

but fail:

As you can see, the last stack is incorrect; oranges are placed in the middle of the apple section. In addition, although it is difficult to notice, there is 1 pixel strip for 0 oranges in the second column, located at 3 along the y axis.

Can someone see what I'm doing wrong, or is there an error with nvd3?

Thank!