Call Director Extension - this makes no sense whatsoever

This has been driving me nuts, the following code sucessfully runs when a call directory extenion is loaded via CXCallDirectoryManager.sharedInstance.reloadExtension()

        let (phoneNumbers, labels) = (["+12061110002", "+12061110003", "+12061110004"], ["A", "B", "C"])
        for (phoneNumber, label) in zip(phoneNumbers, labels)
        {
            context.addIdentificationEntry(withNextSequentialPhoneNumber: phoneNumber, label: label)
        }
        context.completeRequest()

But this code fails:

        let (phoneNumbers, labels) = (["+12065549472", "+12061110003", "+12061110004"], ["A", "B", "C"])
        for (phoneNumber, label) in zip(phoneNumbers, labels)
        {
            context.addIdentificationEntry(withNextSequentialPhoneNumber: phoneNumber, label: label)
        }
        context.completeRequest()

The *only* difference is in the succesful case the first number is "+12061110002" and in the unsucessful case it is "+12065549472".

It fails with error code 4 on beta 10.2 but error code 3 on beta 10.3. Its 100% reproducable, I have two phones, the first code suceedss %100 of the time its run, the seconds code fails %100 of the time it runs.

What on earth could be going on? Why should that number cause it to fail? (This number can be sucesfully added, but only if its added on its own, not in combination with the others at the same time)