WPF Toolkit Chart problems - wpf

Question

I am using WPF Toolkit for charting. I have to problem, that I can't solve:
If I have more than one series in chart. I am using date time axis. Problem is that chart does not display my first column correct. I think image is self explanatory:
I have a checkbox for each of that tree columns. But when I set visibility of the column to Collapsed, the column is just hidden. What I want is, that 2 visible column divide free space between them, so the width will be higher for each column.
Any ideas?
XAML of chart:
<charting:Chart BorderThickness="0"
x:Name="StackedLineChart"
Title=""
Margin="5">
<charting:Chart.Axes>
<charting:DateTimeAxis Interval="1" IntervalType="Months" x:Name="myDateTimeAxis"
Orientation="X" Title="Date">
<charting:DateTimeAxis.AxisLabelStyle>
<Style TargetType="charting:DateTimeAxisLabel">
<Setter Property="StringFormat" Value="{}{0:MMMM}"/>
</Style>
</charting:DateTimeAxis.AxisLabelStyle>
</charting:DateTimeAxis>
<charting:LinearAxis Orientation="Y" ShowGridLines="True" x:Name="myYAxis"
Title="Schedules count"/>
</charting:Chart.Axes>
<charting:Chart.LegendStyle>
<Style TargetType="datavis:Legend">
<Setter Property="Width" Value="0" />
</Style>
</charting:Chart.LegendStyle>
<charting:Chart.Series>
<charting:ColumnSeries ItemsSource="{Binding Data}"
IndependentValuePath="Date"
IsSelectionEnabled="True"
DependentValuePath="1Value">
</charting:ColumnSeries>
<charting:ColumnSeries ItemsSource="{Binding Data}"
IndependentValuePath="Date"
IsSelectionEnabled="True"
DependentValuePath="2Value">
</charting:ColumnSeries>
<charting:ColumnSeries ItemsSource="{Binding Data}"
IndependentValuePath="Date"
IsSelectionEnabled="True"
DependentValuePath="3Value">
</charting:ColumnSeries>
</charting:Chart.Series>
</charting:Chart>