gcc failes to compile operator definition with prefixed namespace

I have operators declared for class my_type in namespace my_namespace.

namespace my_namespace {
 class my_type
 {
  friend std::ostream& operator << (std::ostream& out, my_type t);
 }
}

I'm trying to define these operators in implementation file, but when I write something like that

std::ostream& my_namespace::operator << (std::ostream& out, my_type t)
{
 out << t;
 return out;
}

I get error message

error: ... operator should have been declared inside 'my_namespace'

When I change it to

namespace my_namespace {
    std::ostream& operator << (std::ostream& out, my_type t)
    {
     out << t;
     return out;
    }
}

then it's compiles, but I don't understand the problem. Why does this failed to compile? Is there everything right with that? I would appreciate link to standard as I really don't know what to search.

added

file.h

#ifndef A_H
#define A_H

#include <iosfwd>

namespace N
{
 class A
 {
  friend std::ostream& operator << (std::ostream& out, A& obj);
 };
}

#endif

file.cpp

#include "file.h"
#include <iostream>

std::ostream& N::operator << (std::ostream& out, N::A& obj)
{
 return out;
}

int main() {}

here is complete example. This works fine on VS2010, but gives above mentioned error on gcc 4.4.5.

added

hmm...yes, this one works

namespace N
{
    class A
    {
        friend std::ostream& operator << (std::ostream& out, A& obj);
    };
    std::ostream& operator << (std::ostream& out, A& obj);
}

I was always thinking that in terms of visibility declaring friend operator in class is same thing as declaring outside of the class..looks like it's not. Thanks.

Thanks much in advance.