Question about using auto for type inference of member function pointer

My question is about member function pointer. Here a sample code: class C inherits foo from A and bar from B. I expected both &C::foo and &C::bar are of the same type void (C::*)(), but actually they are different types, one is void(A::*)() and the other is void(B::*)(). I used gdb ptype command to inspected data types.

My question is: is this behavior defined by C++ standards? What is the rationale of this design decision?

#include <type_traits>
#include <iostream>

struct A {
  void foo() {
    std::cout << this << std::endl;
  }
  int a;
};

struct B {
  void bar() {
    std::cout << this << std::endl;
  }
  int b;
};

struct C : public A, B { };

int main() {
  auto p1 = &C::foo;  // p1 is void (A::*)();
  auto p2 = &C::bar;  // p2 is void (B::*)();

  auto p3 = &A::foo;  // p3 is void (A::*)();

  bool b1 = std::is_same<decltype(p1), decltype(p2)>::value;
  bool b2 = std::is_same<decltype(p1), decltype(p3)>::value;
  std::cout << b1 << std::endl; // false
  std::cout << b2 << std::endl; // true
  return 0;
}