Sibling Polymorphism

I've come across a pattern (I'd call it an antipattern) in the course
of my job, recently, and I was wondering:

A: Who's seen or done this before?
B: Is there even a theoretically good reason for something like this?

In simplified form:

// ---------- begin code
class B;

class A
{
public:
    virtual B* getB() = 0;
};

class B
{
public:
    virtual A* getA() = 0;
};

class C : public A, public B
{
public:
    A* getA() { return (A*)this; }
    B* getB() { return (B*)this; }
};

int main()
{
    C* c = new C();
    A* a = c->getA();
    B* b = a->getB();
    a = b->getA();

    delete c;

    return 0;
}
// ---------- end code

If there isn't already a name for this, I think I'd call it "Sideways
Polymorphism."

IMHO, this stinks to high-heaven, but I thought I'd see what the
community experience is--- maybe there's a good reason for this that
I've just never considered. (Note that this software is under active
development and not yet in production-- backward compatibility isn't a
valid excuse, and the same people own A and B.)

-Greg D

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