Custom contact has invalid ContactListId on Windows Universal - contacts

Question

I am experiencing some strange behaviour in the Windows Universal Contacts API. Consider the following method:
public async Task TestContactStore()
{
//Fetch store and create custom contact list
ContactStore localStore = await ContactManager.RequestStoreAsync(ContactStoreAccessType.AppContactsReadWrite);
var list = await localStore.CreateContactListAsync("Contact Store Test");
//Create new contact in custom contact list
await list.SaveContactAsync(new Contact() { Name = "Test", LastName = "Contact"});
ContactStore allAccessStore = await ContactManager.RequestStoreAsync(ContactStoreAccessType.AllContactsReadOnly);
//Print all available contact lists
Debug.WriteLine("All Contact Lists");
var contactLists = await allAccessStore.FindContactListsAsync();
foreach (var contactList in contactLists)
{
Debug.WriteLine(contactList.DisplayName + ": " + contactList.Id);
}
//Print all available contacts
Debug.WriteLine("All Contacts");
var contacts = await allAccessStore.FindContactsAsync();
foreach (var contact in contacts)
{
Debug.WriteLine(contact.Name + " " + contact.LastName + ": " + contact.ContactListId);
}
}
It creates a contact list for my app ("Contact Store Test"). Then it saves a new Contact to this list ("Test Contact"). After this it prints all available contact lists and then all contacts.
The output is:
All Contact Lists
Hotmail: 24,5,5
Contact Store Test: 24,11,11
All Contacts
Hotmail Contact: 24,5,5
Test Contact: 24,5,5
Why does the Test Contact show up with the same ContactListId as the Hotmail-list? In the contacts app on the phone it shows up as belonging to the Contact Store Test-list. What am I missing?

Answer 1

I have now done some further research regarding this behavior. In the latest build 10.0.10512.1000, this behavior has changed. All ContactListId return empty string now.
When fetching contacts the way I did in my example above
var contactLists = await allAccessStore.FindContactListsAsync();
foreach (var contact in contactLists)
{
Debug.WriteLine(contactList.DisplayName + ": " + contactList.Id);
}
It seems as though the contacts in the list are always aggregated contacts (even if they are not linked in the address book). Aggregated contacts (apparently) always has empty ContactListId and AggregateId. The Id-property always matches the AggregateId-property of the corresponding raw contacts.
To get the corresponding contact list id, the raw contacts for that aggregate needs to be fetched:
var contactLists = await allAccessStore.FindContactListsAsync();
foreach (var contact in contactLists)
{
var rawContacts = await allAccessStore.AggregateContactManager.FindRawContactsAsync(aggregateContact);
foreach (var raw in rawContacts)
{
Debug.WriteLine(contactList.DisplayName + ": " + contactList.Id);
}
}
This gives expected ContactListId.