I've set up Virtuoso ODS to provide address book via CardDAV ("virtuoso-opensource" and "virtuoso-vad-ods" packages, version 6.1.6). When I create/edit/delete a contact in kaddressbook ("Contacts" component of Kontact), it is properly synchronized with Virtuoso. However, if a contact is created in Virtuoso, it is not synchronized with kaddressbook (won't appear in the list of contacts). If I edit a contact coming from kaddressbook using the web interface of Virtuoso, it disappears in the contact list of kaddressbook on the next sync.

I presume, kaddressbook adds some metadata to the contacts to help it with sync'ing, but Virtuoso overwrites/wipes it on updates and kaddressbook becomes unable to track them?

Reproducible: Always

Steps to Reproduce:
1. Setup Virtuoso ODS and a "Local CardDAV" in kaddressbook to sync contacts with it (setup details are in "Additional Information" section below).
2. Login to Virtuoso ODS web UI, navigate to "AddressBook", add a contact.
3. Update Address Book folder in kaddressbook - the contact created in Virtuoso does not appear in the list.
4. Add a contact in kaddressbook, visit Virtuoso ODS web UI, Address Book. The contact appears in the list of contacts.
5. Edit the contact in Virtuoso ODS web UI, save changes.
6. Refresh the list of contacts in kaddressbook - the contacts disappears from the list.
Actual Results:  
The contacts created or updated in Virtuoso ODS are not sync'ed with kaddressbook. They just disappear from the list of contacts in kaddressbook (but still remain in Virtuoso ODS).

Expected Results:  
Contacts created in Virtuoso ODS address book should appear in kaddressbook on sync.
Contacts updated in Virtuoso ODS address book should not disappear from kaddressbook.

Virtuoso:
- Install 2 packages "virtuoso-opensource" and "virtuoso-vad-ods".
- (Optional) Make sure "AddressBook" VAD package is installed by visiting Virtuoso Conductor web UI at http://localhost:8890/ > "Conductor" > login using "dba / dba" admin credentials > "System Admin" > "Packages".
- Create an ODS user in "System Admin" > "User Accounts". Make sure "User type" is set to "WebDAV". Note "DAV home page" setting, you'll need it later.

KAddressBook:
- Add Address Book, "DAV Groupware Resource"
- Enter user credentials from Virtuoso ODS user.
- Pick "Configure the resource manually".
- Click "Add", pick "CardDAV", use "http://127.0.0.1:8890/#{ODS_HOME_DIR}/addressbooks/" for "Remote URL", where ODS_HOME_DIR is "DAV home page" string from above. My complete path looks like "http://127.0.0.1:8890/DAV/home/cordawyn/addressbooks/".
- Click "Fetch", pick the only entry from the list below, click "OK".