BUG #9265: why the same interval can't get the same timestamp?

The following bug has been logged on the website:

Bug reference:      9265
Logged by:          yimin
Email address:      miaoyimin@huawei.com
PostgreSQL version: 9.2.6
Operating system:   suse 10.3
Description:

postgres=# select ('epoch'::pg_catalog.timestamptz + 1386201600 * '1
second'::pg_catalog.interval);
        ?column?
------------------------
 2013-12-05 08:00:00+08
(1 row)

postgres=# select ('epoch'::pg_catalog.timestamptz + 16044 * '1
day'::pg_catalog.interval);
        ?column?
------------------------
 2013-12-05 07:30:00+08
(1 row)

postgres=# show timezone;
     TimeZone
-------------------
 Asia/Kuala_Lumpur
(1 row)

postgres=# select * from version();
                                             version
--------------------------------------------------------------------------------------------------
 PostgreSQL 9.2.6 on i686-pc-linux-gnu, compiled by gcc (GCC) 4.1.2 20070115
(SUSE Linux), 32-bit
(1 row)