"AT TIME ZONE" with zone name PostgreSQL bug? I was answering this stackoverflow question and found strange result:

 select * from  pg_timezone_names where name = 'Europe/Berlin' ;
     name      | abbrev | utc_offset | is_dst 
---------------+--------+------------+--------
 Europe/Berlin | CET    | 01:00:00   | f


and next query

select id, 
  timestampwithtimezone, 
  timestampwithtimezone at time zone 'Europe/Berlin' as berlin, 
  timestampwithtimezone at time zone 'CET' as cet 
from data ;
 id  | timestampwithtimezone  |       berlin        |         cet         
 -----+------------------------+---------------------+---------------------
 205 | 2012-10-28 01:30:00+02 | 2012-10-28 01:30:00 | 2012-10-28 00:30:00
 204 | 2012-10-28 02:00:00+02 | 2012-10-28 02:00:00 | 2012-10-28 01:00:00
 203 | 2012-10-28 02:30:00+02 | 2012-10-28 02:30:00 | 2012-10-28 01:30:00
 202 | 2012-10-28 02:59:59+02 | 2012-10-28 02:59:59 | 2012-10-28 01:59:59
 106 | 2012-10-28 02:00:00+01 | 2012-10-28 02:00:00 | 2012-10-28 02:00:00


I'm using PostgreSQL 9.1.2 and ubuntu 12.04.
Just checked that on 8.2.11 result is the same.

According to documentation it doesn't matter if I use name or abbreviation.

Is this a bug?
Am I doing something wrong?
Can someone explain this result?  

EDIT
For the comment that CET is not Europe/Berlin.

I'm just selecting values from pg_timezone_names.

select * from  pg_timezone_names  where abbrev ='CEST';
 name | abbrev | utc_offset | is_dst 
------+--------+------------+--------


and

select * from  pg_timezone_names  where abbrev ='CET';
        name         | abbrev | utc_offset | is_dst 
---------------------+--------+------------+--------
 Africa/Tunis        | CET    | 01:00:00   | f
 Africa/Algiers      | CET    | 01:00:00   | f
 Africa/Ceuta        | CET    | 01:00:00   | f
 CET                 | CET    | 01:00:00   | f
 Atlantic/Jan_Mayen  | CET    | 01:00:00   | f
 Arctic/Longyearbyen | CET    | 01:00:00   | f
 Poland              | CET    | 01:00:00   | f
 .....


During winter Europe/Berlin is +01. During summer it is +02.

EDIT2
In 2012-10-28 timezone has change from summer time to winter time at 2:00.
This two records have the same value in Europe/Berlin:

204 | 2012-10-28 02:00:00+02 | 2012-10-28 02:00:00 | 2012-10-28 01:00:00
106 | 2012-10-28 02:00:00+01 | 2012-10-28 02:00:00 | 2012-10-28 02:00:00


This suggest that if I use one of abbreviations (CET or CEST) for big data range (summer time and winter time) result will be wrong for some of records. Will be good if I use 'Europe/Berlin'.

I changed the system time to '2012-01-17' and pg_timezone_names has changed also.

select * from  pg_timezone_names  where name ='Europe/Berlin';
     name      | abbrev | utc_offset | is_dst 
---------------+--------+------------+--------
 Europe/Berlin | CEST   | 02:00:00   | t
Actually, the documentation says clearly that the time zone name and abbreviation will behave differently.


  In short, this is the difference between abbreviations and full names:
  abbreviations always represent a fixed offset from UTC, whereas most
  of the full names imply a local daylight-savings time rule, and so
  have two possible UTC offsets. Reference


FWIW, that same reference also says


  We do not recommend using the type time with time zone (though it is
  supported by PostgreSQL for legacy applications and for compliance
  with the SQL standard).