Private implementation of public pure virtual

The recent thread "Sanity check: public/private" led me to try
something out which unexpectedly succeeded:

/////////////////////////
#include <iostream>

class B
{
public:
   virtual ~B() {}
   virtual void f() = 0;
};

class D : public B
{
public:
   virtual ~D() {}
private:
   virtual void f() { std::cout << "D::f()" << std::endl;}
};

int main()
{
   D d;
   B* p = &d;
   p -> f();
}
/////////////////////////

This code compiles (and in the latter case runs and produces the
"D::f()" output) with both Comeau online and gcc 4.0.2. I couldn't find
anything in the standard about this, but I'm surprised that neither
compiler at least warns me about what I'm doing here (IMHO I should get
an error).

I don't see how this code could have any practical use, but would
consider it a bug in both compilers...? (The only practical use would
be for hiding away parts of an interface, but then you've got design
issues plus the fact that this just doesn't work).

Comments?

{ See the FAQ item "When should someone use private virtuals?" currently
at <url:
http://www.parashift.com/c++-faq-lite/strange-inheritance.html#faq-23.4>.
-mod }

--
Tarjei Knapstad

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