I've thought that the US government could make a grab for the source code claiming eminent domain. If another country had a local Microsoft office with copies of the source it seems they could do this to. It may seem unreasonable but it actually happens quite a bit.

On case that comes to mind is the Willy's jeep. The design was originally by Willys-Overland but the military took the design and gave it to Ford for production.

The needs of the many (i.e. government) often come before those of the individual