Getting GUID of group with IADs interface - winapi

Question

I'm using the following C++ code to get all groups for a user:
(from https://msdn.microsoft.com/en-us/library/windows/desktop/aa746342(v=vs.85).aspx. I just added a few liens to get the group GUID as well)
HRESULT CheckUserGroups(IADsUser *pUser)
{
IADsMembers *pGroups;
HRESULT hr = S_OK;
hr = pUser->Groups(&pGroups);
pUser->Release();
if (FAILED(hr)) return hr;
IUnknown *pUnk;
hr = pGroups->get__NewEnum(&pUnk);
if (FAILED(hr)) return hr;
pGroups->Release();
IEnumVARIANT *pEnum;
hr = pUnk->QueryInterface(IID_IEnumVARIANT, (void**)&pEnum);
if (FAILED(hr)) return hr;
pUnk->Release();
// Enumerate.
BSTR bstr;
VARIANT var;
IADs *pADs;
ULONG lFetch;
IDispatch *pDisp;
VariantInit(&var);
hr = pEnum->Next(1, &var, &lFetch);
while (hr == S_OK)
{
if (lFetch == 1)
{
pDisp = V_DISPATCH(&var);
pDisp->QueryInterface(IID_IADs, (void**)&pADs);
pADs->get_Name(&bstr);
printf("Group belonged: %S\n", bstr);
SysFreeString(bstr);
pADs->get_GUID(&bstr);
printf("Group guid: %S\n", bstr);
SysFreeString(bstr);
pADs->Release();
}
VariantClear(&var);
pDisp = NULL;
hr = pEnum->Next(1, &var, &lFetch);
};
hr = pEnum->Release();
return S_OK;
}
int main()
{
CoInitialize(NULL);
CComPtr<IADsUser> pUser;
std::wstring ADpathName = std::wstring(L"WinNT://domain/user");
if( ADsGetObject(ADpathName.c_str(), IID_IADsUser, (void**)&pUser) == S_OK )
{
CheckUserGroups(pUser);
}
return 0;
}
However, the GUID for all groups is the same and doesn't reflect the real group GUID. why is that?