BUG #4960: Unexpected timestamp rounding

The following bug has been logged online:

Bug reference:      4960
Logged by:          Matthias
Email address:      matthias.cesna@gmail.com
PostgreSQL version: 8.3.7
Operating system:   Windows XP
Description:        Unexpected timestamp rounding
Details:

Dear developers,

I noticed an unusual (and from my point of view inconsistent) rounding of a
timestamp:

It is about when using a upper-boundary timestamp. The value of 9999-12-31
23:59:59.999999 is sometimes used to indicate an infinite validity. However
passing such a value in an SQL will lead it to be rounded up:

DDB02=# select timestamp '9999-12-31 23:59:59.999999';
      timestamp
----------------------
 10000-01-01 00:00:00
(1 row)

This is not logical to me since 23:59:59.999999 would be a valid value or?
This also happens during the insert into a table and as such modifies my
intention and the data.

Doing the same with the year 2000 does not give me any rounding:

DDB02=# select timestamp '2000-12-31 23:59:59.999999';
         timestamp
----------------------------
 2000-12-31 23:59:59.999999

Thank you for having a look at the issue & sincerely thank you for such a
great database!

Regards,
Matthias