Only last control in Data Template column getting updated

Question

I have a DataTemplate Column with 2 DatePickers that are bound to 2 properties. When the data in these control is changed only last control gets updated

        <sdk:DataGridTemplateColumn Width="300"  CanUserReorder="False" >              
         <sdk:DataGridTemplateColumn.CellTemplate>
               <DataTemplate>
                 <Grid MouseRightButtonDown="ActionsGrid_MouseRightButtonDown" Width="300" Height="40" MouseLeftButtonDown="ActionsGrid_MouseLeftButtonDown">
                        <StackPanel Orientation="Horizontal">
                             <TextBlock VerticalAlignment="Stretch" Width="100" Text="{Binding Start,  Converter={StaticResource DateConverter}}"
                                         Padding="2" HorizontalAlignment="Center" />
                             <TextBlock VerticalAlignment="Stretch" Width="100" Text="{Binding Due, Converter={StaticResource DateConverter}}"
                                         Padding="2" HorizontalAlignment="Center" />
                         </StackPanel>
                  </Grid>
                </DataTemplate>                                                  
          </sdk:DataGridTemplateColumn.CellTemplate>
    <sdk:DataGridTemplateColumn.CellEditingTemplate>
               <DataTemplate>
                     <StackPanel Orientation="Horizontal">
                       <sdk:DatePicker VerticalAlignment="Top" Width="100" SelectedDate="{Binding Start, Mode=TwoWay,}" Padding="2" />
                       <sdk:DatePicker VerticalAlignment="Top" Width="100" SelectedDate="{Binding Due, Mode=TwoWay, ValidatesOnDataErrors=True}"  Padding="2" />
                     </StackPanel>
               </DataTemplate>  
     </sdk:DataGridTemplateColumn.CellEditingTemplate>
   </sdk:DataGridTemplateColumn>

In this case if I update both Start and Due Only Due gets updated. Also the binding works fine because if I put a breakPoint on Start in my Model class it gets hit but the value passed is the original value of Start

EDIT 1

After some debugging I found out that If I only have one control inside my DataTemplate it works Fine. Also When I change the Date The break point is hit straightaway. But if I have more than one control the break point is not hit until I focus out of column and then only the last binding works.

EDIT 2

After some mroe debugging I noticed that it will work fine if I only use CellTemplate and discard cell EditTemplate

     <sdk:DataGridTemplateColumn Width="300"  CanUserReorder="False" >              
             <sdk:DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                   <StackPanel Orientation="Horizontal">
                       <sdk:DatePicker VerticalAlignment="Top" Width="100" SelectedDate="{Binding Start, Mode=TwoWay,}" Padding="2" />
                       <sdk:DatePicker VerticalAlignment="Top" Width="100" SelectedDate="{Binding Due, Mode=TwoWay, ValidatesOnDataErrors=True}"  Padding="2" />
                  </StackPanel>
               </DataTemplate>  
     </sdk:DataGridTemplateColumn.CellEditingTemplate>
   </sdk:DataGridTemplateColumn>

EDIT 3

private void DatePicker_SelectedDateChanged(object sender, SelectionChangedEventArgs e)
        {
            (sender as DatePicker).GetBindingExpression(DatePicker.SelectedDateProperty).UpdateSource();
        }

I was able to refresh binding on both the control using the selectedDatechange event and then refreshing the binding on the sender.

I am still not sure why the 2 way binding working won't work.

Can anyone explain why this is happening?

EDIT 4

Model and Properties

 public DateTime? Start 
        { 
            get { return _Start; } 
            set 
            { 
                _Start = value; Dirty = true; 

                if (_Start.HasValue && _Due.HasValue && _Start.Value > _Due.Value)
                    _dataErrors["Start"] = "Start date cannot be greater than the Due date";
                else
                    if (_dataErrors.ContainsKey("Start"))
                        _dataErrors.Remove("Start");
                NotifyPropertyChanged(); NotifyPropertyChanged("CalcStatus");
            } 
        }
        public DateTime? Due 
        { 
            get { return _Due; } 
            set 
            { 
                _Due = value; Dirty = true; 
                if (_Start.HasValue && _Due.HasValue && _Start.Value > _Due.Value)
                    _dataErrors["Start"] = "Start date cannot be greater than the Due date";
                else
                    if (_dataErrors.ContainsKey("Start"))
                        _dataErrors.Remove("Start");
                NotifyPropertyChanged("Due"); NotifyPropertyChanged("CalcStatus");
            }
        }

Answer 1

Alright I think I finally have fixed it. I am still not 100% sure why it wasnt working but I'll create a new small project and try to find out the reason.

What happened was that I modified my NoitifyPropertyChangedEvent by passing it[CallerMemberName] so that the name of the property calling it is passed automatically. Which means if I change the name property for example "Start" I don't have to worry about updating NotifyPropertyChanged("Start").

 public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged([CallerMemberName] string propertyName =null)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

This worked fine for all properties except for when I had a DataTemplateColumn. Converting it back to standard code and passing the propertyName explicitly fixed my issue.

public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }