Starting Windows Vista, Windows Server 2008 and Windows 7, to prevent address scans of IPv6 addresses based on the known company IDs of network adapter manufacturers, Windows by default generate random interface IDs for non-temporary autoconfigured IPv6 addresses, including public and link-local addresses. A public IPv6 address is a global address that is registered in DNS and is typically used by server applications for incoming connections, such as a Web server.
However, this can cause issues with some connection instances in which case you may need to disable this option.