Nullable<>.HasValue and unnecessary select from select

from grandChild in db.GrandChild
from child in db.Child
where grandChild.ChildID.HasValue
select grandChild;

generate 

SELECT
	t3.ParentID as ParentID1,
	t3.ChildID as ChildID1,
	t3.GrandChildID as GrandChildID1
FROM
	(
		SELECT   -- what is it ????
			t1.ChildID,
			t1.ParentID,
			t1.GrandChildID
		FROM
			GrandChild t1,
			Child t2
	) t3
WHERE
	t3.ChildID IS NOT NULL

I think, bltoolkit should generate 
SELECT
  t1.ChildID,
  t1.ParentID,
  t1.GrandChildID
FROM
  GrandChild t1,
  Child t2
t1.ChildID IS NOT NULL