I use .Net 3.5, Winforms, Databinding
I have derived classes, the base class implements IPropertychanged
public event PropertyChangedEventHandle
I know it is too late to answer, but this problem can be solved, if you set event when your binding should change value, if you set it on property value change event your problem will be solved. You can do this by this way
textBox.DataBindings.Add("textBoxProperty", entity, "entityProperty", true, DataSourceUpdateMode.OnPropertyChanged);