Intentionally different args?

Line 28 in 04bbe81

    
           PropertyChanged?.Invoke(this, new PropertyChangedExtendedEventArgs(propertyName, oldValue, newValue));

The event args you pass into PropertyChanged doesn't match the event args passed into PropertyChangedExtended. If this is intentional, add a comment explaining why you're doing something weird. If it's accidental, I recommend creating just a single PropertyChangedExtendedEventArgs object and using it for both invokes.