Rails does not detect primary key value with postgres when not using sequences

Rails does not detect the primary key value of new saved objects when the primary key is not a sequence, and the value is generated by another default function.

                         Table "public.moo"
 Column |         Type          |              Modifiers
--------+-----------------------+-------------------------------------
 id     | uuid                  | not null default uuid_generate_v4()
 moo    | character varying(64) |
Indexes:
    "moo_pkey" PRIMARY KEY, btree (id)

This works perfectly when using the postgresql command line;

INSERT INTO moo(moo) VALUES('moo') RETURNING id;
                  id
--------------------------------------
 9a5374a9-0bf3-4196-b68b-e1dd6ab69f69
(1 row)

INSERT INTO moo(moo) VALUES('moo') RETURNING id;
                  id
--------------------------------------
 a107f5da-f013-4c15-83e8-fb0220fa3918
(1 row)

etc..

When using the framework the id isn't retrieved:

irb(main):006:0> blah = Moo.create(:moo => 'testing123')
=> #<Moo id: nil, moo: "testing123">

irb(main):007:0> Moo.find_by_moo('testing123')
=> #<Moo id: "c4c3ea70-61d9-4d4b-baae-aa6adde0b58b", moo: "testing123">

Tested with Rails 3.0.3 and PostgreSQL 8.3.12.