help understanding collation order

hi,

postgresl-8.4.6 (database encoding is utf8)

the following sql behaves strangely on one of my servers:

create table ttt(id serial not null primary key, name text);
insert into ttt (name) values ('CLARKE, DAVID');
insert into ttt (name) values ('CLARK, PETER');
insert into ttt (name) values ('CLARKE');
insert into ttt (name) values ('CLARK');
select * from ttt order by name;
drop table ttt;

the behaviour i expect (and see on macosx-10.6.6) is:

id | name
----+---------------
4 | CLARK
2 | CLARK, PETER
3 | CLARKE
1 | CLARKE, DAVID

the behaviour i don't expect but see anyway (on debian-5.0) is:

id | name
----+---------------
4 | CLARK
3 | CLARKE
1 | CLARKE, DAVID
2 | CLARK, PETER

the "good" server has lc_messages='en_AU' and the
"bad" server has lc_messages="en_AU.utf8" which may
be relevant but i can't successfully alter these
values (i.e. postgres doesn't restart after i try)
so i'm hoping it's not relevant.

can anyone explain what i've done wrong here and
suggest what i can do to fix it?

cheers,
raf

p.s. the postgres installation was PostgresPlus/8.4SS that
was subsequently upgraded via postgres one click installers.