emplace_back() issue under VS2013

Consider the following codes

std::vector<int> nums{21, 22, 23, 24};
nums.emplace_back(nums[0]);
nums.emplace_back(nums[1]);

for (auto n : nums) {
    std::cout << n << std::endl;
}

Output of VS2013

21
22
23
24
-17891602
22

Why the -17891602 is here?

Output of GCC 4.8.4is correct as following

21
22
23
24
21
22

Then I compare the implementation of emplace_back between VS2013 and GCC

VS2013

template<class... _Valty>
    void emplace_back(_Valty&&... _Val)
    {   // insert by moving into element at end
    if (this->_Mylast == this->_Myend)
        _Reserve(1);
    _Orphan_range(this->_Mylast, this->_Mylast);
    this->_Getal().construct(this->_Mylast,
        _STD forward<_Valty>(_Val)...);
    ++this->_Mylast;
    }

GCC

template<typename _Tp, typename _Alloc>
template<typename... _Args>
  void
  vector<_Tp, _Alloc>::
  emplace_back(_Args&&... __args)
  {
    if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
      {
        _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
                                 std::forward<_Args>(__args)...);
        ++this->_M_impl._M_finish;
      }
    else
      _M_emplace_back_aux(std::forward<_Args>(__args)...);
  }

It seems the weird _Reserve(1); is used in VS2013. Why?