Lambdas and capture by reference local variables : Accessing after the scope

I am passing my local-variables by reference to two lambda. I call these lambdas outside of the function scope. Is this undefined ?

std::pair<std::function<int()>, std::function<int()>> addSome() {
    int a = 0, b = 0;
    return std::make_pair([&a,&b] {
        ++a; ++b;
        return a+b;
        }, [&a, &b] {
            return a;
        });
}

int main() {
    auto f = addSome();
    std::cout << f.first() << " " << f.second();
    return 0;
}

If it is not, however, changes in one lambda are not reflected in other lambda.

Am i misunderstanding pass-by-reference in context of lambdas ?

I am writing to the variables and it seems to be working fine with no runtime-errors with output

2 0. If it works then i would expect output 2 1.