Time zone specifications, abbreviations vs full names

Either I am exceptionally confused, or the documentation in 8.5.3 appears to be wrong. Could someone clarify what I'm missing?

The documentation states: "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." "PST" is given as a specific example of an abbreviation in this case. But it appears that using "PST" gives you a time zone rule:

CREATE TABLE t (
z TIMESTAMP WITH TIME ZONE
);

insert into t values ( '2011-03-13 01:00 PST'::timestamptz);
insert into t values ( '2011-03-13 01:00-7'::timestamptz );
update t set z = z + '2 hours'::interval;

select * from t;
z
------------------------
2011-03-13 04:00:00-07
2011-03-13 03:00:00-07
(2 rows)

--

But if "PST" really did imply a fixed offset, shouldn't the results be the same?

--
-- Christophe Pettus
xof(at)thebuild(dot)com