How do I reject a change in an editable Xceed Wpf DataGrid cell?

Question

I have an Xceed DataGridControl on a WPF Window with a few columns that are data bound to a DataTable. The UpdateSourceTrigger on the grid control is set to CellContentChanged so that the binding source updates as soon as a cell's content changes.

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="375" Width="494" xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"&gt;
    <Grid>
        <xcdg:DataGridControl Margin="22,21,25,27" Name="MyTable" UpdateSourceTrigger="CellContentChanged" CellEditorDisplayConditions="MouseOverCell, CellIsCurrent">
            <xcdg:DataGridControl.View>
                <xcdg:TableView />
            </xcdg:DataGridControl.View>
            <xcdg:DataGridControl.Columns>
                <xcdg:Column FieldName="ProductID" Title="ProductID" IsMainColumn="True" />
                <xcdg:Column FieldName="Description" Title="Description" />
                <xcdg:Column FieldName="IsObsolete" Title="IsObsolete" />
            </xcdg:DataGridControl.Columns>
        </xcdg:DataGridControl>
    </Grid>
</Window>

I added some code to handle the DataTable ColumnChanging event. In the event handler, I added some validation to prevent the "IsObsolete" column's value from ever being set to True.

If I simply change the proposed value to False, the data source change is effectively rejected; however, the visual display of the checkbox in the grid remains checked until the user moves away from the row. (By the way, calling e.Row.RejectChanges() surprisingly does not reject the change at all.)

The effect I want to achieve is for the checkbox never to appear checked if the validation fails.

This is what I've got so far:

Imports System.Data

Class Window1

    Private _dt As System.Data.DataTable

    Private Sub Window1_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded

        _dt = New System.Data.DataTable("MyTable")
        MyTable.ItemsSource = _dt.DefaultView

        PopulateDataTable()

        AddHandler _dt.ColumnChanging, AddressOf HandleStatusChanges

    End Sub

    Private Sub HandleStatusChanges(ByVal sender As Object, ByVal e As DataColumnChangeEventArgs)
        If String.Compare(e.Column.ColumnName, "IsObsolete", True) = 0 _
        AndAlso CBool(e.ProposedValue) Then
            e.ProposedValue = False
        End If
    End Sub

    Private Sub PopulateDataTable()

        _dt.Columns.Add(New System.Data.DataColumn("ProductID", GetType(String)))
        _dt.Columns.Add(New System.Data.DataColumn("Description", GetType(String)))
        _dt.Columns.Add(New System.Data.DataColumn("IsObsolete", GetType(Boolean)))

        Dim dr As System.Data.DataRow
        For row = 1 To 5
            dr = _dt.NewRow
            dr("ProductID") = "SB-" & row
            dr("Description") = "Longboard"
            dr("IsObsolete") = False
            _dt.Rows.Add(dr)
        Next

        _dt.AcceptChanges()

    End Sub

End Class

Thanks in advance!