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(at)huawei(dot)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)