Bug or Short between my brain and the keyboard?

Just thought I'd try the cluster command.  What am I doing wrong.
ReadHat 5.0
6.3.1 rpm's

[djackson@www]$ psql template1
Welcome to the POSTGRESQL interactive sql monitor:
  Please read the file COPYRIGHT for copyright terms of POSTGRESQL

   type \? for help on slash commands
   type \q to quit
   type \g or terminate with semicolon to execute query
 You are currently connected to the database: template1

template1=> \d
Couldn't find any tables, sequences or indices!
template1=> \l
datname  |datdba|datpath
---------+------+---------
template1|   100|template1
postgres |   100|postgres
(2 rows)

template1=> create database test;
CREATEDB
template1=> \connect test
connecting to new database: test
test=> create table list (k int2);
CREATE
test=> insert into list values (1);
INSERT 33769 1
test=> insert into list select max(k)+1;
.
.
.
test=> select * from list;
k
-
1
2
3
4
5
6
(6 rows)

test=> create table list2 (k1 int2 NOT NULL, k2 int2 NOT NULL);
CREATE
test=> create UNIQUE INDEX l1 ON list2(k1, k2);
CREATE
test=> create UNIQUE INDEX l2 ON list2(k2, k1);
CREATE
test=> insert into list2 select l1.k, l2.k from list as l1, list as l2;
INSERT 0 36
test=> select * from list2;
k1|k2
--+--
 1| 1
 2| 1
 3| 1
.
.
.
 4| 6
 5| 6
 6| 6
(36 rows)

test=> vacuum verbose analyze list2;
NOTICE:  Rel list2: Pages 1: Changed 0, Reapped 0, Empty 0, New 0; Tup
36: Vac 0, Crash 0, UnUsed 0, MinLen 44, MaxLen 44; Re-using:
Free/Avail. Space 0/0; EndEmpty/Avail. Pages 0/0. Elapsed 0/0 sec.
NOTICE:  Ind l2: Pages 2; Tuples 36. Elapsed 0/0 sec.
NOTICE:  Ind l1: Pages 2; Tuples 36. Elapsed 0/0 sec.
VACUUM
test=> cluster l1 on list2;
ERROR:  Cannot create unique index. Table contains non-unique values
test=> cluster l2 on list2;
PQexec() -- Request was sent to backend, but backend closed the channel
before responding.
        This probably means the backend terminated abnormally before or
while processing the request.