Daryl Herzmann <akrherz(at)iastate(dot)edu> writes:
> akrherz=# create table test (day date);
> CREATE
> akrherz=# insert into test values('2000_04_02');
> INSERT 13166281 1
> akrherz=# insert into test values('2000_04_01');
> INSERT 13166282 1
> akrherz=# insert into test values('2000_04_03');
> INSERT 13166283 1
Would that be a daylight-savings transition date in your timezone?
If so, this is a known date-to-timestamp conversion bug. It's fixed
for 7.1.
regards, tom lane