IUnknown* B;
IUnknown* C;
A->QueryInterface(IID_ISomeInterface, (void**)B);
// B refcount = 1.

A->QueryInterface(IID_ISomeInterface, (void**)C);
// C refcount = 1, B refcount unchanged.

C->Release();
// C refcount = 0, C is destroyed, B refcount unchanged.

C->SomeMethod(); // Will crash as C has been destroyed, even though there is an outstanding 'live' ISomeInterface instance on the same object (i.e. B).