Non-pointer typedef of member functions not allowed?

After getting an answer to this question I discovered there are two valid ways to typedef a function pointer.

typedef void (Function) ();
typedef void (*PFunction) ();

void foo () {}

Function * p = foo;
PFunction  q = foo;

I now prefer Function * p to PFunction q but apparently this doesn't work for pointer-to-member functions. Consider this contrived example.

#include <iostream>

struct Base {
    typedef void (Base :: *Callback) ();
                        //^^^ remove this '*' and put it below (i.e. *cb)
    Callback cb;

    void go () {
        (this->*cb) ();
    }

    virtual void x () = 0;

    Base () {
        cb = &Base::x;
    }
};

struct D1 : public Base {
    void x () {
        std :: cout << "D1\n";
    }
};

struct D2 : public Base {
    void x () {
        std :: cout << "D2\n";
    }
};  

int main () {
    D1 d1;
    D2 d2;
    d1 .go ();
    d2 .go ();
}

But if I change it to the new preferred style: typedef void (Base :: Callback) () and Callback * cb, I get a compiler error at the point of typedef

extra qualification 'Base::' on member 'Callback'

Demo for error.

Why is this not allowed? Is it simply an oversight or would it cause problems?