BUG #7942: Timestamp "19991231 240000" should not be out of range

The following bug has been logged on the website:

Bug reference:      7942
Logged by:          Georg Kindermann
Email address:      georg.kindermann@gmx.at
PostgreSQL version: 9.1.8
Operating system:   Debian Wheezy
Description:        =


select cast('19991231 240000' as timestamp);
--Produces >ERROR:  timestamp out of range<

select cast('20000101 000000' as timestamp);
--Works

--For other years both styles work e.g
select cast('19981231 240000' as timestamp);
select cast('19990101 000000' as timestamp);

--1999 to 2000 is no Leap second. Is there something other special? Thanks!