you were not using your CellEditors because columns were read only and Dont use textboxes in CellContentTemplate use TextBlock
<xcdg:Column Title="GL Code" FieldName="GLCode" Width="100">
<xcdg:Column.CellContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding}"/>
</DataTemplate>
</xcdg:Column.CellContentTemplate>
<xcdg:Column.CellEditor>
<xcdg:CellEditor>
<xcdg:CellEditor.EditTemplate>
<DataTemplate>
<TextBox Text="{xcdg:CellEditorBinding}"/>
</DataTemplate>
</xcdg:CellEditor.EditTemplate>
</xcdg:CellEditor>
</xcdg:Column.CellEditor>
</xcdg:Column>
<xcdg:Column Title="Deferred GL Code" FieldName="DeferredGLCode" Width="100">
<xcdg:Column.CellContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding}"/>
</DataTemplate>
</xcdg:Column.CellContentTemplate>
<xcdg:Column.CellEditor>
<xcdg:CellEditor>
<xcdg:CellEditor.EditTemplate>
<DataTemplate>
<TextBox Text="{xcdg:CellEditorBinding}"/>
</DataTemplate>
</xcdg:CellEditor.EditTemplate>
</xcdg:CellEditor>
</xcdg:Column.CellEditor>
</xcdg:Column>