That sounds like a fairly weak argument, because IP protections still apply to open source, except for trade secrets. The degree of protection is dictated by a

That sounds like a fairly weak argument, because IP protections still apply to open source, except for trade secrets. The degree of protection is dictated by a project's license, or if in the absence of a license then a nation's default copyright status. In your first ReactOS example from 2006 it wasn't even Microsoft that discovered or claimed the problematic code violation. It doesn't look like Microsoft was involved at all.