tsvector/tsearch equality and/or portability issue issue ?

We just had a complaint on IRC that:

devel=# select 'blah foo bar'::tsvector = 'blah foo bar'::tsvector;
?column?
----------
f
(1 row)

and that searches for certain values would not return all matches under
some circumstances.

a little bit of testing shows the following:

postgres=# create table foo (bla tsvector);
CREATE TABLE
postgres=# insert into foo values ('bla bla');
INSERT 0 1
postgres=# insert into foo values ('bla bla');
INSERT 0 1
postgres=# select bla from foo group by bla;
bla
-------
'bla'
(1 row)

postgres=# create index foo_idx on foo(bla);
CREATE INDEX
postgres=# set enable_seqscan to off;
SET
postgres=# select bla from foo group by bla;
bla
-------
'bla'
'bla'
(2 rows)

postgres=# set enable_seqscan to on;
SET
postgres=# select bla from foo group by bla;
bla
-------
'bla'
(1 row)

ouch :-(

I can reproduce that at least on OpenBSD/i386 and Debian Etch/x86_64.

It is also noteworthy that the existing regression tests for tsearch2 do
not seem to do any equality testing ...

Stefan