Does std::string move constructor actually move?

So here i got a small test program:

#include <string>
#include <iostream>
#include <memory>
#include <vector>

class Test
{
public:
  Test(const std::vector<int>& a_, const std::string& b_)
    : a(std::move(a_)),
      b(std::move(b_)),
      vBufAddr(reinterpret_cast<long long>(a.data())),
      sBufAddr(reinterpret_cast<long long>(b.data()))
  {}

  Test(Test&& mv)
    : a(std::move(mv.a)),
      b(std::move(mv.b)),
      vBufAddr(reinterpret_cast<long long>(a.data())),
      sBufAddr(reinterpret_cast<long long>(b.data()))
  {}

  bool operator==(const Test& cmp)
  {
    if (vBufAddr != cmp.vBufAddr) {
      std::cout << "Vector buffers differ: " << std::endl
        << "Ours: " << std::hex << vBufAddr << std::endl
        << "Theirs: " << cmp.vBufAddr << std::endl;
      return false;
    }

    if (sBufAddr != cmp.sBufAddr) {
      std::cout << "String buffers differ: " << std::endl
        << "Ours: " << std::hex << sBufAddr << std::endl
        << "Theirs: " << cmp.sBufAddr << std::endl;
      return false;
    }
  }

private:

  std::vector<int> a;
  std::string b;
  long long vBufAddr;
  long long sBufAddr;
};

int main()
{
  Test obj1 { {0x01, 0x02, 0x03, 0x04}, {0x01, 0x02, 0x03, 0x04}};
  Test obj2(std::move(obj1));

  obj1 == obj2;


  return 0;
}

Software i used for test:

Compiler: gcc 7.3.0

Compiler flags: -std=c++11

OS: Linux Mint 19 (tara) with upstream release Ubuntu 18.04 LTS (bionic)

The results i see here, that after move, vector buffer still has the same address, but string buffer doesn't. So it looks to me, that it allocated fresh one, instead of just swapping buffer pointers. What causes such behavior?