Possible old and fixed bug in Postgres?

I was looking at perl CPAN Module (DateTime::Format::Pg) and saw that it did
something that seemed odd to me with time zones, based on the comment:

    # For very early and late dates, PostgreSQL always returns times in
    # UTC and does not tell us that it did so.

Early is before 1901-12-14 and late after 2038-01-18

A quick test setting my time zone to be America/Chicago I got

select '1900-01-01 00:00:00'::timestamptz;
      timestamptz
------------------------
 1900-01-01 00:00:00-06
(1 row)

and

select '2040-01-01 00:00:00'::timestamptz;
      timestamptz
------------------------
 2040-01-01 00:00:00-06

These seemed correct to me. I'm guessing this might have been a bug/feature of
pg in the long ago.

Steve