So if I'm not mistaken, "Party" (capital P) refers to a national signatory of the TPP, right? As opposed to "some guy out there." Wouldn't that mean that this would prevent nation-states from requiring copyleft in order to use or distribute that software? Is there even a threat of that? Or is this perhaps relating to potential requirements that you for example share your source code with the Chinese government in order to sell to customers there?

EDIT: As opposed to, for example, GPL requirements that are imposed on individuals by individuals, not TPP Parties.