Dates Show Up Without Data

While this data is correct there is an unessicary date duplicate on the X axis.

using System.Windows.Controls;
using Adapt.Model.TaskManagement;
using System;
using Adapt.Model.TaskManagement.Custom;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using ActiproSoftware.Windows.Controls.Charts.Primitives;
using ActiproSoftware.Windows.Controls.Charts;
using System.Linq;
using System.Diagnostics;

namespace HoursChart
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {

            //Generate random cost data
            var random = new Random();
            var dataSize = 5;
            var costs = new List<CostInfoCustom>();
            for (int i = 0; i < 10; i++)
            {
                costs.Add(new CostInfoCustom { Qty = random.Next(1, dataSize), CostDate = new DateTime(2012, 01, random.Next(1, dataSize), 12, 0, 0), TaskInfoKey = new TaskInfo { TaskNo = random.Next(1, dataSize) } });
            }

            //Set the chart to use the generated cost data
            SetChartData(costs);
        }

        private void SetChartData(List<CostInfoCustom> costs)
        {
            InitializeComponent();

            //Set the X origin to 0, the interval to 1 hour and display a maximum of 24 hours
            HourChart.YAxes.Add(new XYDecimalAxis { Minimum = 0, TickMajorInterval = 1, Maximum = 24 });
            HourChart.IsLegendVisible = true;

            //Group costs by date and get all the task numbers from the data
            var costsByDates = costs.GroupBy(c => c.CostDate);
            var allTaskNumbers = costs.Select(x => x.TaskInfoKey.TaskNo);

            //For each day add qty = 0 records where a task is missing for that day
            foreach (var costsByDay in costsByDates)
            {
                var missingTaskNumbers = allTaskNumbers.Except(costsByDay.Select(x => x.TaskInfoKey.TaskNo)).ToList();
                foreach (int taskNumber in missingTaskNumbers)
                {
                    costs.Add(new CostInfoCustom { Qty = 0, CostDate = costsByDay.Key, TaskInfoKey = new TaskInfo { TaskNo = taskNumber } });
                }
            }

            //group the costs by task
            var costsGroupedByTaskNo = costs.GroupBy(c => c.TaskInfoKey.TaskNo);

            //for each task's costs, create a data series.
            foreach (var taskCosts in costsGroupedByTaskNo)
            {
                //DEBUG
                Debug.WriteLine("TaskNo: " + taskCosts.Key + " - Total Hours: " + taskCosts.Sum(x => x.Qty) + " On Days: " + string.Join(", ", taskCosts.Select(cg => cg.CostDate.Day).Distinct()));

                HourChart.Series.Add(new BarSeries { ItemsSource = taskCosts.ToList(), YPath = "Qty", XPath = "CostDate", StackKind = XYSeriesStackKind.Normal, Description = "Task No " + taskCosts.Key });
            }
        }
    }

}

<UserControl
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
  xmlns:charts="http://schemas.actiprosoftware.com/winfx/xaml/charts" 
  xmlns:controlsToolkit="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Toolkit"
  xmlns:chartingToolkit="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit"
  x:Class="HoursChart.MainPage">

    <UserControl.Resources>
        <Style TargetType="charts:XYChart">
            <Setter Property="Width" Value="1000" />
            <Setter Property="Height" Value="900" />
        </Style>
    </UserControl.Resources>

    <Grid>
        <charts:XYChart Name="HourChart"/>
    </Grid>

</UserControl>