Problem with intervals

I'm getting an unexpected result using intervals in an expression:

select ('2003-10-26 0:00:00'::timestamp + '1 day'::interval)::date;    date
------------ 2003-10-26
(1 row)

When I get rid of the date cast it becomes clear what is happening:

select '2003-10-26 0:00:00'::timestamp + '1 day'::interval;        ?column?
------------------------ 2003-10-26 23:00:00-08
(1 row)

I assumed '1 day' would always increment the date by 1, but it appears 
that '1 day' just means '24 hours', and due to the daylight/standard 
time shift, October 26 was 25 hours long this year.

Is this a Postgres bug, or is this correct SQL behavior?  I'm running 
Postgres 7.2.2.

Bob S.