The NLA feature of Windows Server from 2008, R2 and 2012 has always been a bit frustrating and puzzling as to how it arbitrarily decides where it will place a given network card on multi-homed servers.
We often run into this in clustered environments, where there's no gateways or DCs for Windows to talk to, and thus Microsoft decides to lock things up tighter than can be.
While reading the blogs lately, we recently found the following useful article on various approaches to help resolve this issue by at least forcing things onto the Private location instead of Public. A variety of methods are outlined from GPO to registry.
Full Article here:
Windows Server – Force Your Network Connection to Where it Belongs