Based on CodePLex discussion https://wpftoolkit.codeplex.com/discussions/351469.
If a propertyItem from an expandable PropertyItem is modified, and the parent PropertyItem uses it in its ToString() method, we should update the parent PropertyItem editor to reflect the modification.
If a propertyItem from an expandable PropertyItem is modified, and the parent PropertyItem uses it in its ToString() method, we should update the parent PropertyItem editor to reflect the modification.