WITH and exclusive locks

Hi,

When conducting performance tests of our application, I saw quite a few
exclusive locks in SELECTs with WITH clause. So I created a big table and
executed a query which takes time.
with x as (select * from emp where first_name like 'Sco%')
select * from x;
I got 2 locks - one accesshare lock against the table and one ExclusiveLock
with out any database/relation.
2417 postgres 10/95 10/95 ExclusiveLock Yes
2013-11-23 17:38:58+05:30

My guess is that the Exclusive lock is against some in-memory structure
(the temp table created by the WITH clause) and hence is not an issue. Is
that correct?
Regards,
Jayadevan