That result is incorrect, unexpected, and bizarre.
PostgreSQL 9.2.4 produces the correct result.
regress=> select * from test;
t_date
---------------------
2013-08-20 00:00:00
2013-08-20 00:00:00
(2 rows)
as does 8.3, the oldest version I can be bothered testing.
Whatever patched / hacked up version of PostgreSQL you're using has introduced a bug.