This HAS to be UB...

Keep in mind that I am a C programmer; well, anyway here is the C++
program...
______________________________________________________________________
#include <cstdio>
#include <cstdlib>
#include <new>

struct custom_allocator {
  static void* allocate(std::size_t size)
  throw(std::bad_alloc()) {
    void* const mem = ::operator new(size);
    std::printf("custom_allocator::allocate(%p, %lu)\n",
      (void*)mem, (unsigned long)size);
    return mem;
  }

  static void deallocate(void* const mem, std::size_t size)
   throw() {
    std::printf("custom_allocator::deallocate(%p, %lu)\n",
      (void*)mem, (unsigned long)size);
    ::operator delete(mem);
  }
};

template<typename T>
struct allocator_base {
  static void* operator new(std::size_t size)
   throw(std::bad_alloc()) {
    return custom_allocator::allocate(size);
  }

  static void* operator new[](std::size_t size)
   throw(std::bad_alloc()) {
    return custom_allocator::allocate(size);
  }

  static void operator delete(void* mem)
   throw() {
    if (mem) {
      custom_allocator::deallocate(mem, sizeof(T));
    }
  }

  static void operator delete [](void* mem, std::size_t size)
   throw() {
    if (mem) {
      custom_allocator::deallocate(mem, size);
    }
  }
};

template<std::size_t T_size>
class buf {
  char mem[T_size];
};

class buf2 : public buf<1234>, public allocator_base<buf2> {
  char mem2[1000];
};

int main() {
  buf2* b = new buf2;
  delete b;

  b = new buf2[5];
  delete [] b;

  return 0;
}
______________________________________________________________________

On GCC I get the following output:

custom_allocator::allocate(00246C50, 2234)
custom_allocator::deallocate(00246C50, 2234)
custom_allocator::allocate(00247760, 11174)
custom_allocator::deallocate(00247760, 11174)

On MSVC 8 I get:

custom_allocator::allocate(00362850, 2234)
custom_allocator::deallocate(00362850, 2234)
custom_allocator::allocate(00366B68, 11170)
custom_allocator::deallocate(00366B68, 2234)

Are they both right due to UB? WTF is going on? GCC seems to be accurate at
least... DAMN!

thank you all for your time.