When trying to copy an address from one DAV collection to another, the address appears in the collection as expected, however is never synced to the server.
Both collections are sitting on the same server but belong to different users.
In Akonadi Console, the following is logged:

NotificationManager::notify ( Item (23354, b23353) in collection 134 added )
AgentBase(akonadi_davgroupware_resource_8): Unable to add item: There was a problem with the request. The item has not been created on the server. An unexpected error (412) occurred while attempting to upload https://ingo@ratsdorf.dyndns.org/groupdav.php/ingo/addressbook-family/addressbook-490-cbd2bc7d9e888bb71460725c836b157f.vcf. (412).

Reproducible: Always

Steps to Reproduce:
1. Copy address from one DAV server collection to another
2. Address appears as expected
3. Address is never synced to the server however stays in the destination collection
Actual Results:  
Address appears as expected, destination collection, however is never synced to the server.


Expected Results:  
The address is copied to the destination and synced or an error displayed and the destination address deleted again.

Since the original UUID is copied, the server rejects the creation in the other collection with the same UUID.
However Akonadi/Kaddrssbook does not delete the destination address and it stays in there as a dead entry that will neve sync. No feedback is given to the user, the destination address is not deleted.

Suggested action (either or):
a) if destination is on same server, either copy the address without UUID thus allowing its creation. Or display a warning about same UUID on same server and let user decide whether he wants to copy anyway.
b) Or try to store destination address and if error occurs, delete destination address thus avoiding dead entry.

Only workaround to copy address at this stage is to export address, edit it and delete UUID from VCF file, save and import into destination collection.

I have set this report to critical because it actually causes the loss of data.
Image a user copied addresses from one collection to another, the deletes the original collection. All data gone since it will never sync the destination data and will never show a warning.