Problem with join fetch

[Michael Simons]

Hello,

Assume three classes A (1:N) B (1:N) C:
class A { List<B> bs; }
class B { List<C> cs; }

Why is the following query denied?

select a from A a join fetch a.bs join fetch a.bs.cs;

Also denied:
select a from A a join fetch a.bs b join fetch b.cs;

Why doesn't this create an SQL statement like

select ... from A inner join B inner join C

thanks for any hints,
Michael