Is there an immutable ID to use with the UWP Contact Picker?

Question

Contacts do not appear to keep the same ID after edits. In a UWP app:

1. Launch custom UWP app, user clicks "Add Contact"
2. Call contactPicker.PickContactAsync()
3. User selects contact, returns a Contact with an ID such as {5.70002.836}
4. Save Contact ID
5. Close UWP app
6. Launch People, change contact picture, close People
7. Launch custom UWP app
8. Call contactStore.GetContactAsync(savedContactId) <- this returns null
9. Call contactPicker.PickContactAsync(), select same contact
10. Returned correct Contact, however, ID is now {5.70002.849}

Is that the correct behavior? Is there some other way of tracking the same contact in a UWP app between sessions?