Relation ordering in FROM clause causing error related to missing entry... Or not.

Hi all,

Today while playing with some queries I bumped into the following thing:
=# with count_query as (select generate_series(0,1) as a) select b
from count_query, generate_series(1, count_query.a) as b;b
---1
(1 row)
=# with count_query as (select generate_series(0,1) as a) select b
from generate_series(1, count_query.a) as b, count_query;
ERROR:  42P01: missing FROM-clause entry for table "count_query"
LINE 1: ...eries(0,1) as a) select b from generate_series(1, count_quer...
             ^
 
LOCATION:  errorMissingRTE, parse_relation.c:2850

I have been a little bit surprised by the fact that different entry
ordering in the FROM clause of the main query had different effects.
Perhaps there is something I am missing? I haven't looked at the code
but if this happens to be a bug I am fine to submit a patch.
Regards,
-- 
Michael