std::function constructor and nullptr

Why does the following code prints "0" as the output?

#include <functional>
#include <iostream>

int main()
{
    typedef void (*fp_t)();

    fp_t fp = nullptr;

    std::function<void()> f = fp;
    std::cout << (f == nullptr) << '\n';
}

I've tested it both with gcc 4.7.2 and MSVC-11.0.

I think that it's should print "1" because of the following quote from the standard:

ISO/IEC 14882:2011

20.8.11.2.1 function construct/copy/destroy [func.wrap.func.con]

template<class F> function(F f);
template<class F, class A> function(allocator_arg_t, const A& a, F f);

...

8 Postconditions: !*this if any of the following hold: — f is a NULL function pointer. — f is a NULL pointer to member. — F is an instance of the function class template, and !f