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This is not a bug. All the reported functions expect va_list argument 
to be initialized before being called. AFAICT, they are consistently 
used in this way. For example,
PyObject *
PyObject_CallFunctionObjArgs(PyObject *callable, ...)
{
 PyObject *args, *tmp;
 va_list vargs;
 if (callable == NULL)
 return null_error();
 /* count the args */
 va_start(vargs, callable);
 args = objargs_mktuple(vargs);
 va_end(vargs);
 if (args == NULL)
 return NULL;
 tmp = PyObject_Call(callable, args, NULL);
 Py_DECREF(args);
 return tmp;
}
This may need to be clarified in the docs. For example, PyString_FromFormatV does not mention that vargs needs to be 
initialized: <http://docs.python.org/dev/c-
api/string.html#PyString_FromFormatV>. On the other hand, this may be 
obvious to most C programmers.
I suggest to close this issue as invalid.