Control Refresh Not Working on AddNew

When binding a control to a BindingSource and executing .AddNew on the
binding source, then setting default values on the row, the bound controls do
not show the default values until .ReadValue() is called from the control
binding, even though ControlUpdateMode is set to OnPropertyChanged:

ParticipantDS.ParticipantRow row =
(ParticipantDS.ParticipantRow)((DataRowView)participantBindingSource.Current).Row;

row.LastName="Smith";

lastNameTextBox.DataBindings["Text"].ReadValue();

How do I get the control to show the value without explicitly calling
ReadValue?

Thanks