After selecting a date from datepicker, the new value doesn't get saved in the grid. It defaults back to whatever date was before

Below is the grid xaml code 

<xcdg:Column FieldName="CompletedDate" Title="CompletedDate" Width="110">

<xcdg:Column.CellEditor>

<xcdg:CellEditor>

<xcdg:CellEditor.EditTemplate>

<DataTemplate>

<xcdg:DatePicker Name="dpCompletedDate" Background="{DynamicResource LightBrush}" Foreground="{DynamicResource TextBlockForeGround}" HorizontalAlignment="Left" Height="20" Width="100" />

</DataTemplate>

</xcdg:CellEditor.EditTemplate>

</xcdg:CellEditor>

</xcdg:Column.CellEditor>

</xcdg:Column>

 Does any one have a solution for this? Whats going wrong here?