TextBox that shipped with the .net 3.5 release had a bug, fixed in later versions, that prevents to set the
UndoLimit property to 0, Radical provides a behavior as a workaround:
<TextBox Text="bla bla..."><i:Interaction.Behaviors><behaviors:DisableUndoManagerBehavior /></i:Interaction.Behaviors></TextBox>
the behavior is defined in the
http://schemas.topics.it/wpf/radical/windows/behaviors xml namespace.