I tried to reproduce this on both Windows 2012 and Windows 2012 R2 but couldn’t get the same end result.
I can confirm the initial validation error (An unknown error occurred while validating the server.), and I can see the strange query for . IN SOA, but clicking “OK” at that point appears to work (no further errors are shown and the forwarding zone is added).
It appears that the second error message that you encountered (A problem occurred while trying to add the conditional forwarder. A zone configuration problem occurred.) may be unrelated to the strange validation behavior.
I can’t really tell why it is doing its validation based on a query for . IN SOA but it appears to be mostly a cosmetic problem as you’re not prevented from proceeding despite the validation failure.