BUG #5672: Can't input julian days BC

The following bug has been logged online:

Bug reference:      5672
Logged by:          Benjamin Gigot
Email address:      therealvaldor@hotmail.com
PostgreSQL version: 8.4.4
Operating system:   Ubuntu
Description:        Can't input julian days BC
Details:

After trying to enter Confucius birthday (28th September 551BC) I had the
following error :

Query failed: ERROR: date/time field value out of range: "J1520447"

I then used a psql to try to enter different dates in the Julian days
format.

The date down to 0001-01-01 is working :

test=> INSERT INTO datetest (date) VALUES ('J1721426');
INSERT 0 1

But then under that it's not working anymore :

test=> INSERT INTO datetest (date) VALUES ('J1721425');
ERROR:  date/time field value out of range: "J1721425"
LINE 1: INSERT INTO datetest (date) VALUES ('J1721425');

Documentation specify that dates can go down to J0, that is 4713BC.

Am I missing something ?