I have the following association

ObjectA ---Many-to-many---ObjectB (unidirectional A to B)
ObjectC is a subclass of ObjectB

I use lazy initialization, and the same classes as proxies.

I add a set of objectCs to ObjectA and save the graph.

When I read this graph, I loop through the set of ObjectBs (which are in this case all ObjectCs), all of them are of type:

mypackage.ObjectB$$EnhancerByCGLIB$$d991a4fd

I believe this the proxy class. The problem is when I check real instances I get this unexpected result:

instanceof ObjectB returns true (expexted)

instanceof ObjectC returns false ???

Is this normal or am I missing someting?

When I use one-to-many assocaiation, getClass() returns mypackage.ObjectB (Without $$EnhancerByCGLIB$...), and everything works as expected.

This is expected. It's explains at 12.1.
The expected class is of ClassB, so hibernate will proxy ClassB.
Proxying is done by extending ClassB. While being extended, it cannot be of ClassC (no multiple inheritance in Java).

Actually this makes sense. We load ObjectBs as proxies. ObjectB proxies are subclasses of ObjectB. They are unware of ObjectC.

But why do we have proxies for many-to-many and not for one-to-many?

But why do we have proxies for many-to-many and not for one-to-many?

This also makes sense.

In one-to-many, Hibernate may be using find query: Looking for foreign keys in many side table.

In many-to-many, Hibernate is using find to find the many side primary keys in the association table, then using load query to get the many side objects (since it knows their primary keys).