confusing inheritance

I'm trying to get going with this objekt oriented concept but managed to
get confused right from the start.
Basically I know what it's all about with OO from programming languages
but look:

I started pgAdmin and entered something like

TABLE myObjects (
ObjectID int4 PRIMARY KEY,
createdOn timestamp,
createdByUserID int4
)

then

TABLE myTerminatedObjects (
validFrom timestamp,
validUntil timestamp
) INHERITS myObjects

I inserted an object with ObjectID = 0 into myOjects.
Then I inserted a record in myTerminatedObjects again with ObjectID=0
since I supposed that myTerm... only inherited the structure of myObjects.

As expected myTerm... had one record.
But myObjects held 2 records both with 0 in the ObjectID column, which I
thought to be impossible because it is the primary key of myObjects.

Obviously myTerminatedObjects stores it's values of inherited fields in
the tablespace of myObjects breaking myObjects integrity without
PostgreSQL complainig about.
Am I right ?

And myTerm... inherits the field "ObjectID" but not in the function as
primary key so it has no key at all ?
At least MS-Access 2K told me so.

May someone give me a pointer to whats going on, please ?

... Andreas

System:
Win 2K
PostgreSQL 7.2.2 as service
Access 2K as client
pgAdminII 1.2.0 as client