Is std::bind ignoring superfluous arguments standard-conforming?

The functor returned by std::bind ignores superfluous arguments [SO1, SO2, SO3]. A simple example looks as follows.

#include <iostream>
#include <functional>

void foo(int a) {
  std::cout << "a=" << a << std::endl;
}

int main() {
  auto f = std::bind(foo, 42);
  f(3141); // a=42
}

It is clear that implementing std::bind in this way is easier [SO1a]. Is, however, this ignoring of superfluous arguments standardized or undefined behavior?