Well, adjusting for time zone, I still don't get an expected result:

$ export TZ=UTC
$ date -r 1136073599; date -r 1136073600
Sat Dec 31 23:59:59 UTC 2005
Sun Jan  1 00:00:00 UTC 2006

Where is Sat Dec 31 23:59:60 UTC 2005, as promised in
src/share/zoneinfo/leapseconds?

#                                    UTC TIME STEP
#                             on the 1st of January 2006
#
# A positive leap second will be introduced at the end of December 2005.
# The sequence of dates of the UTC second markers will be:
#
#                       2005 December 31,     23h 59m 59s
#                       2005 December 31,     23h 59m 60s
#                       2006 January   1,      0h  0m  0s

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert      -- You author it, and I'll reader it.
\X/ rhialto/at/xs4all.nl        -- Cetero censeo "authored" delendum esse.