boost::in_place_factory produces warning

[NN]

Visual C++ 9.0, Warning level 4

#include <boost/utility/in_place_factory.hpp>
#include <boost/optional.hpp>

#include <boost/noncopyable.hpp>

struct x : boost::noncopyable
{
public:
        static void init(int i);
        
private:
        x(int i) : i (i)
        {
        }

        friend boost::in_place_factory1<int>;

        int i;
};

boost::optional<x> x_instance;

void x::init(int i)
{
        x_instance = boost::in_place(i);
}

1>boost\utility\in_place_factory.hpp(68): warning C4512: 'boost::in_place_factory1<A0>' : assignment operator could not be generated
1>          with
1>          [
1>              A0=int
1>          ]
1>          a.cpp(26) : see reference to class template instantiation 'boost::in_place_factory1<A0>' being compiled
1>          with
1>          [
1>              A0=int
1>          ]