indexing of INT8 ?

hi
i just checked a friends database and it seems that INT8 fields are not
indexable.
i mean:
he has a table with several fields. one of this fields is int8 with unique
index.
we have aproximately 100000 records in this table, database is vacuumed, but
the index doesn't seem to work when i do something like

explain select * from table where int8field = xxxx;

is it known bug of 7.1.2 or is something wrong with the database?

depesz

--
hubert depesz lubaczewski                          http://www.depesz.pl/
------------------------------------------------------------------------
... and the end of all our exploring  will be to arrive where we started
and know the place for the first time.                    -- T. S. Eliot