Using bind1st for a method that takes argument by reference

I have a struct like this:

struct A {
    void i(int i) {}
    void s(string const &s) {}
};

Now when I try this:

bind1st(mem_fun(&A::i), &a)(0);
bind1st(mem_fun(&A::s), &a)("");

The first line compiles OK, but the second generates an error:

c:\program files (x86)\microsoft visual studio 10.0\vc\include\xfunctional(299): error C2535: 'void std::binder1st<_Fn2>::operator ()(const std::basic_string<_Elem,_Traits,_Ax> &) const' : member function already defined or declared
          with
          [
              _Fn2=std::mem_fun1_t<void,A,const std::string &>,
              _Elem=char,
              _Traits=std::char_traits<char>,
              _Ax=std::allocator<char>
          ]
          c:\program files (x86)\microsoft visual studio 10.0\vc\include\xfunctional(293) : see declaration of 'std::binder1st<_Fn2>::operator ()'
          with
          [
              _Fn2=std::mem_fun1_t<void,A,const std::string &>
          ]
          c:\work\sources\exception\test\exception\main.cpp(33) : see reference to class template instantiation 'std::binder1st<_Fn2>' being compiled
          with
          [
              _Fn2=std::mem_fun1_t<void,A,const std::string &>
          ]

What could be the problem? How could I fix it?

Edit:

It seems that any reference argument is a problem. So if I change the i method to void i(int &i) {} I get a similar error.