vs2013 vc++ bug?

maybe_bug.cpp

/////VS 2013 /////
//////////////////
#include "stdafx.h"
#include <assert.h>
#include <thread>

#define __thread_local __declspec(thread)

const int some_int = 5;

struct _thread_local_data
{
    std::thread::id thread_id;
    int int_val;
    void initialize()
    {
       thread_id = std::this_thread::get_id();
       int_val = some_int;
    }
};

__thread_local _thread_local_data data;

static int static_initialize()
{
    data.initialize();
    return 0;
}

static int val = static_initialize();

int _tmain(int argc, _TCHAR* argv[])
{
    auto this_id = std::this_thread::get_id();
    auto x = data.int_val;

    assert(x == some_int);

    //assert fails here
    assert(this_id == data.thread_id);

    return 0;
}

__thread_local _thread_local_data data;

_thread_local_data& ensure_thread_data() {
    if (data.int_val == 0)
        data.initialize();
    return data;
}

int _tmain(int argc, _TCHAR* argv[])
{
    auto data = ensure_thread_data();

    auto this_id = std::this_thread::get_id();
    auto x = data.int_val;

    assert(x == some_int);

    //assert fails here
    assert(this_id == data.thread_id);

    return 0;
}