> APIs and their implementations (and their use) is full of bugs, and unless forced to programs generally don't get it right. This shows that programs are derivative by default.
No, it only shows that _if_ a program depends on the bugs in a particular implementation, rather than an API common to all implementation, then it might be derivative.
If this sort of dependency is as common as you say then it shouldn't be difficult to prove that the application is derivative of the library implementation rather than just the API--but you still need to prove it for each specific application and library, not just assume it to be true "by default".