Returning an implemented interface

Hi,

in my library I have a situation like this where the coclass
implements IA, IB and IDisp:

[
 object,
 uuid(.....),
 oleautomation,
 nonextensible,
 pointer_default(unique)
]
Interface IA : IUnknown
{
  methodA(...)
}

[
 object,
 uuid(.....),
 oleautomation,
 nonextensible,
 pointer_default(unique)
]
Interface IB : IUnknown
{
  methodB(...)
}

[
  dual,
  nonextensible,
  hidden
]
Interface IDisp : IDispatch
{
  HRESULT Get_IA([out, retval] IA** pVal);
  HRESULT Get_IB([out, retval] IB** pVal);
}

library MyLib
{
.....
    [
        uuid(AB566C81-AF54-11DE-B5BE-00A0D15E9B20),
        helpstring("AudioLib Class")
    ]
    coclass MyClass
    {
                Interface IA;
                Interface IB;
                [default] interface IDisp;
    };
}

The implementation of the IDisp Get methods are:

STDMETHODIMP CMyClass::Get_IA(IA** pVal)
{
  if (!pVal) return E_POINTER;
  return this->QueryInterface(IID_IA, reinterpret_cast<void**>
(&pVal));
};

//------------------------------------------------------------------------------

STDMETHODIMP CMyClass::Get_IB(IB** pVal)
{
  if (!pVal) return E_POINTER;
  return this->QueryInterface(IID_IB, reinterpret_cast<void**>
(&pVal));
};

Now when, in a VB6 client, I do this:

---------------------------------------------------------------
Dim p As MyClass

Private Sub Form_Load()
  Set p = New MyClass
End Sub

Private Sub Form_Unload(Cancel As Integer)
  Set p = Nothing
End Sub
---------------------------------------------------------------

The object is created and destroyed well, but if I call Get_IB or
Get_IA:

---------------------------------------------------------------
Private Sub Form_Load()
  Set p = New MyClass
  With p.Get_IB
     ' No code here....
  End With
End Sub

Private Sub Form_Unload(Cancel As Integer)
  Set p = Nothing
End Sub
---------------------------------------------------------------

The object p is not destroyed (the MyClass::FinalRelease is not
called).
Why this happens? Where I wrong?

Thanks,
Daniele.