problem (bug?) with "in (subquery)"

I have the following query that isn't behaving like I would expect:

select * from strains s where s.id in (select strain_id from pathway_strains);

I would expect each strain record to appear only once.  Instead I get output 
like this, where the same strain id appears many times:
 id   |     name     | organism
-------+--------------+----------   83 | common       |       82    83 | common       |       82    83 | common       |
     82    83 | common       |       82    83 | common       |       82    83 | common       |       82    83 | common
    |       82    83 | common       |       82    83 | common       |       82    83 | common       |       82   506 |
common      |      487  506 | common       |      487
 
... continues

By the way, this output is the same as if running the query:
select * from strains s join pathway_strains ps on ps.strain_id = s.id;

=====================================
Table "public.strains"   Column     |     Type     |                        Modifiers
---------------+--------------+---------------------------------------------------------id            | integer      |
notnull name          | text         | not null default 'common'::textorganism      | integer      | not null
 

Indexes:   "strains_pkey" PRIMARY KEY, btree (id)
================================== View "public.pathway_strains"  Column   |  Type   | Modifiers
------------+---------+-----------pathway_id | integer |strain_id  | integer |
View definition:SELECT DISTINCT p.id AS pathway_id, c.strain_id  FROM catalyst_associations c  JOIN pathway_edges e ON
c.pathway_edge_id= e.id  RIGHT JOIN pathways p ON p.id = e.pathway_id ORDER BY p.id, c.strain_id;
 

The contents of pathways_strains are likepathway_id | strain_id
------------+-----------      2083 |        76      2083 |        80      2083 |        83      2083 |        95
2084|        76      2084 |        80      2084 |        83      2084 |        95      2084 |       162
 
...etc

So, am I wrong in expecting each strain record to appear only once in the 
result set?  Or is there something wrong with PostgreSQL?  I would be happy 
to provide more information if it's needed.

Thank you!

Luca

ps: # select version();                                                    version

-----------------------------------------------------------------------------------------------------------------PostgreSQL
8.0.3on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 3.2.3 
 
20030502 (Red Hat Linux 3.2.3-42)