Error: [ngRepeat:dupes] on a seemingly valid object

Question

I am getting a duplicate keys error

This object gives me the error:

$scope.workoutData = {
    "2015-02-01":[["16:22:45","2","7","270","1"]],
    "2015-06-11":[["18:34:10","2","8","225","1"]],
    "2015-06-22":[["18:30:45","1","8","185","1"]]
};

But this one does not:

$scope.workoutData = {
    "2015-02-01":[["16:22:45","2","7","270","1"]],
    "2015-06-11":[["18:34:10","2","8","225","1"]]
};

Here is my HTML

       <div id="calendar" ng-controller="calendarCtrl">
            <div id="owl-demo" class="owl-carousel owl-theme">
                <div class="item" ng-repeat="(date, figures) in workoutData track by $index">
                    <div class="scollHeader">
                        {{date}}
                    </div>
                    <div class="scrollBody">
                        <table class="table">
                            <thead>
                                <tr>
                                    <th>Time</th>
                                    <th>Exercise</th>
                                    <th>Reps</th>
                                    <th>Weight</th>
                                    <th>Location</th>

                                </tr>
                            </thead>
                            <tbody>
                                <tr ng-repeat="set in figures">
                                    <td ng-repeat="dataPoint in set">{{dataPoint}}</td>

                                </tr>
                            </tbody>
                        </table>
                    </div>
                </div>
            </div>
        </div>

When the larger object is used, <div class="item" ng-repeat="(date, figures) in workoutData track by $index"> properly repeats 3 times, but the data is not added to the 3rd <div>

What is it about "2015-06-22":[["18:30:45","1","8","185","1"]] that gives me this error?