WPF Datagrid TemplateColumn unable to get textbox to update database

I am binding this to a datatable in code using

  dataGrid1.ItemsSource = dTable.DefaultView

and have a button that saves the changes using the SqlDataAdapter update method dAdapter.Update(dTable)

The problem is that I want to disable editing the IC_DEF_CHAR_TEXT field when the record isNumeric and the IC_DEF_CHAR_TEXT when the record IsText. I tried binding to the IsReadOnly property but found that it is not bindable, so I created templates for the two fields and bound the IsEnabled property to the IsText and IsNumeric fields.

<DataGrid AutoGenerateColumns="False" HorizontalAlignment="Left" Margin="27,42,0,0" Name="dataGrid1" VerticalAlignment="Top"  AreRowDetailsFrozen="True">
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding KEY}" Visibility="Hidden" IsReadOnly="True"></DataGridTextColumn>
            <DataGridTextColumn Binding="{Binding CHARACTERISTIC_CODE}" Header="Unit" IsReadOnly="True" />
            <DataGridTextColumn Binding="{Binding UNIT_CHAR}" Header="Unit" IsReadOnly="True" />
            <DataGridTemplateColumn Header="Numeric" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBox  Text="{Binding Path=IC_DEF_CHAR_NUMERIC, Mode=TwoWay}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
                <DataGridTemplateColumn.CellEditingTemplate>
                <DataTemplate>
                        <TextBox IsReadOnly="False"  Text="{Binding Path=IC_DEF_CHAR_NUMERIC, Mode=TwoWay,  UpdateSourceTrigger=PropertyChanged}" />
                </DataTemplate>
                </DataGridTemplateColumn.CellEditingTemplate>
            </DataGridTemplateColumn>
            <DataGridTemplateColumn Header="Text" >
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBox Text="{Binding Path=IC_DEF_CHAR_TEXT, Mode=TwoWay}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
                <DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <TextBox Text="{Binding Path=IC_DEF_CHAR_TEXT, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellEditingTemplate>
            </DataGridTemplateColumn>
        </DataGrid.Columns>

This worked exactly like I wanted, the textboxes were enabled when necessary. However the changes made in the TextBoxes are no longer saved to the database during update. Can someone out there explain to me why the database is no longer being updated?