Dereferencing a function with default arguments - C++14 vs C++11

Following code can't be compiled with g++ version 5.4.0 with option -std=c++1y:

void f(int=0) ;

int main() {
    f(); // ok
    (*f)(2);// ok
    (*f)();// ok c++11; error with c++14: too few arguments to function
    return 0;
}

The function declared to have default argument, so what is wrong here? thanks for help.

And why does g++ -c -std=c++11 compile?