BUG #6605: wrong type cast from timestamp to timestamptz

The following bug has been logged on the website:

Bug reference:      6605
Logged by:          Sergey Burladyan
Email address:      eshkinkot@gmail.com
PostgreSQL version: 9.1.3
Operating system:   Debian testing
Description:=20=20=20=20=20=20=20=20

Postgres from Debian package:
PostgreSQL 9.1.3 on x86_64-unknown-linux-gnu, compiled by gcc (Debian
4.6.3-1) 4.6.3, 64-bit

Good:
set timezone to 'Europe/Moscow'; select  '2011-03-27
23:00:00'::timestamptz;
SET
=D0=92=D1=80=D0=B5=D0=BC=D1=8F: 0,092 =D0=BC=D1=81
      timestamptz=20=20=20=20=20=20=20
------------------------
 2011-03-27 23:00:00+04

Bad:
set timezone to 'W-SU'; select  '2011-03-27 23:00:00'::timestamptz;
SET
=D0=92=D1=80=D0=B5=D0=BC=D1=8F: 0,106 =D0=BC=D1=81
      timestamptz=20=20=20=20=20=20=20
------------------------
 2011-03-28 02:59:54+04

Good again:
set timezone to 'W-SU'; select  '2011-03-27 23:00:01'::timestamptz;
SET
=D0=92=D1=80=D0=B5=D0=BC=D1=8F: 0,135 =D0=BC=D1=81
      timestamptz=20=20=20=20=20=20=20
------------------------
 2011-03-27 23:00:01+04

For information, 2011-03-27 the last day when Daylight Saving Time was used.
After it Daylight Saving Time is canceled in Russia:

W-SU is symlink:
$ ls -la /usr/share/zoneinfo/Europe/Moscow=20
lrwxrwxrwx 1 root root 7 =D0=9C=D0=B0=D1=80  6 22:39 /usr/share/zoneinfo/Eu=
rope/Moscow ->
../W-SU

$ zdump -v W-SU | tail
W-SU  Sat Oct 24 22:59:59 2009 UTC =3D Sun Oct 25 02:59:59 2009 MSD isdst=
=3D1
gmtoff=3D14400
W-SU  Sat Oct 24 23:00:00 2009 UTC =3D Sun Oct 25 02:00:00 2009 MSK isdst=
=3D0
gmtoff=3D10800
W-SU  Sat Mar 27 22:59:59 2010 UTC =3D Sun Mar 28 01:59:59 2010 MSK isdst=
=3D0
gmtoff=3D10800
W-SU  Sat Mar 27 23:00:00 2010 UTC =3D Sun Mar 28 03:00:00 2010 MSD isdst=
=3D1
gmtoff=3D14400
W-SU  Sat Oct 30 22:59:59 2010 UTC =3D Sun Oct 31 02:59:59 2010 MSD isdst=
=3D1
gmtoff=3D14400
W-SU  Sat Oct 30 23:00:00 2010 UTC =3D Sun Oct 31 02:00:00 2010 MSK isdst=
=3D0
gmtoff=3D10800
W-SU  Sat Mar 26 22:59:59 2011 UTC =3D Sun Mar 27 01:59:59 2011 MSK isdst=
=3D0
gmtoff=3D10800
W-SU  Sat Mar 26 23:00:00 2011 UTC =3D Sun Mar 27 03:00:00 2011 MSK isdst=
=3D0
gmtoff=3D14400
W-SU  9223372036854689407 =3D NULL
W-SU  9223372036854775807 =3D NULL

I also see this problem in my other server with 9.0:
select  '2011-03-27 23:00:00'::timestamptz;
      timestamptz=20=20=20=20=20=20=20
------------------------
 2068-04-02 03:00:00+04
(1 row)