Presumably if there were any IP rights at all (what with it being a Communist state), they were assigned to the USSR government or, like products of the US government, are born into the public domain.
The "made by gov't -> public domain" is an USA-specific detail that doesn't apply in most other places.
If specific people owned the copyright, then it's as usual for any other works; if a specific USSR institution owned the copyright, then the ownership will be determined by the early 1990ies transition/reorganization laws and contracts; if 'USSR' owned it, then it's owned by Russia afterwards, not public domain.
If the governments still care, let them deal with it. It's no business of yours, nor do you need to white-knight on their behalf and throw in irrelevant arguments & gratuitious nationalist slurs.
http://www.cendi.gov/publications/04-8copyright.html
The fact that U.S. Government works are not protected under the U.S. Copyright Law does not create a requirement that all U.S. Government works be made publicly available without restriction (See Gellman, Robert M. Twin Evils: Government Copyright and Copyright-like Controls Over Government Information. Syracuse Law Review, 999, 1995. ADA394923). See Pfeiffer v. Central Intelligence Agency 62, 60 F.3d 861 (D.C. Cir. 1995). Federal laws and agency policies govern the public release of U.S. Government information. Examples include Executive Order 13292, Classified National Security Information , OMB Circular A-130,63 Management of Federal Information Resources, Department of Defense Directive 5230.9 Clearance of DoD Information for Public Release, April 9, 1996, ASD (PA) and DOD Instruction 5230.29 Security and Policy Review of DoD Information for Public Release.