Destructor not called when object on stack is overwritten

Today I was wondering about c++ destructors so I wrote a small test program. That answered my original question but raised a new one which is:
The following program:

#include "stdafx.h"
#include <vector>
#include <iostream>
using namespace std;
class test
{
public:
    int id;
    vector<test> collection;
    test(){}
    test(int id_in){id = id_in;}
    ~test(){cout << "dying: " << id << "\n";}
};

int _tmain(int argc, _TCHAR* argv[])
{
    {
        test obj(1);
        obj.collection.push_back(test(2));
        obj.collection.push_back(test(3));
        cout << "before overwrite\n";
        obj = test(4);
        cout << "before scope exit\n";
    }
    int x;
    cin >> x;
}

produces the following output:

dying: 2
dying: 2
dying: 3
before overwrite
dying: 2
dying: 3
dying: 4
before scope exit
dying: 4

Why don't I see a destructor for my test object with id 1? If its destructor isn't called when it is overwritten, than what calls the destructors of the instances in its vector?