vector::push_back insists on using copy constructor though a move constructor is provided

I was receiving a strange error from gcc and cannot figure out why. I made the following example code to make the problem more clear. Basically, there is a class defined, for which I make its copy constructor and copy assignment operator private, to prevent calling them accidentally.

#include <vector>
#include <cstdio>
using std::vector;

class branch 
{
public:
  int th;

private:
  branch( const branch& other );
  const branch& operator=( const branch& other );

public:

  branch() : th(0) {}

  branch( branch&& other )
  {
    printf( "called! other.th=%d\n", other.th );
  }

  const branch& operator=( branch&& other )
  {
    printf( "called! other.th=%d\n", other.th );
    return (*this);
  }

};



int main()
{
  vector<branch> v;
  branch a;
  v.push_back( std::move(a) );

  return 0;
}

I expect this code to compile, but it fails with gcc. Actually gcc complains that "branch::branch(const branch&) is private", which as I understand shouldn't be called.

The assignment operator works, since if I replace the body of main() with

branch a;
branch b;
b = a;

It will compile and run as expected.

Is this a correct behavior of gcc? If so, what's wrong with the above code? Any suggestion is helpful to me. Thank you!