VS2010 C++ wrong subtraction result (1.0f - 1.0f == 1753.0) when code optimization is on by szpilewski

//This code result is 1.0f - 1.0f == 1753.0

#include "stdafx.h" //empty
#include <tchar.h>
#include <iostream>
#include <stdlib.h>

struct Struct
{
float a;
float b;
};

int _tmain(int argc, _TCHAR* argv[])
{
Struct* ptr = new Struct;

float x;
float y = rand() ? 1.0f : 2.0f;

x = y + 1753;

ptr->a = x;
ptr->b = x - y;

x = y;

std::cout << "x = " << x << std::endl;
std::cout << "y = " << y << std::endl;

float result = x - y;

std::cout << "x - y = " << result << std::endl;
std::cin.get();

delete ptr;
return 0;
}