PostgreSQL wrong converting from timestamp without time zone to timestamp with time zone

I faced with the following issue this morning:

select '2011-12-30 00:30:00'::timestamp without time zone AT TIME ZONE 'EST5EDT';

returns me 2011-12-30 05:30:00+00 witch is wrong.

But next queries below:

select '2011-12-30 00:30:00'::timestamp without time zone AT TIME ZONE 'UTC-5';
select '2011-12-30 00:30:00' AT TIME ZONE 'EST5EDT';

i see right date 2011-12-29 19:30:00

Preventing your question about my local timezone:

SELECT  current_setting('TIMEZONE');
current_setting
-----------------
     UTC
(1 row)

Do anyone have answer why postgresql converts timestamp without time zone some weird way and instead taking away 5 hours it adds instead?

Copyright Notice：Content Author:「saicheg」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/21277170/postgresql-wrong-converting-from-timestamp-without-time-zone-to-timestamp-with-t