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.