Julian Day 0 question

Ran across something that is confusing me.  The docs for to_char
indicates that julian day 0 is January 1, 4712 BC at midnight.

http://www.postgresql.org/docs/8.3/static/functions-formatting.html

When I run to_char, I don't get 0 for that date.

postgres=# select to_char('4712-01-01 BC'::date, 'J');
  to_char
---------
  404

I get julian day 0 for 4714-11-24 BC.

postgres=# select to_char('4714-11-24 BC'::date, 'J');
  to_char
---------
  0

Output of 'select version()'

PostgreSQL 8.3devel on x86_64-unknown-linux-gnu, compiled by GCC gcc
(GCC) 4.1.1 20070105 (Red Hat 4.1.1-52)

andrew