ps: I established this bug. It is not windows but VC 8 which behaves
different with VC 7.
I have mailed this to Michael M (Microsoft).
BSTR __cdecl Format(PCWSTR pszFormat, ...) throw()

{

va_list args;

HRESULT hr = S_OK;

BSTR retVal = NULL;
va_start( args, pszFormat );

int len = _vscwprintf( pszFormat, args );

retVal = SysAllocStringLen(NULL, len);

if(retval != NULL)

vswprintf( retVal, (SIZE_T)len, pszFormat, args );

va_end(args);

return retVal;

}

INT main()

{

CoInitialize(NULL);

{

   BSTR test = Format(L"%s, %d,%s", L"one", 2, L"three");

   wprintf(test); //"output one, 2, thre" <-- BUG this used to have the
correct length in VC 7?

   SysFreeString(test);

}

CoUninitialize();

return 0;

}