Many-to-many association not stored in NHibernate

Many-to-many association not stored in NHibernate

I'll try to explain the problem precisely.
There's an entity A which has a one-to-many relation with B (a collection).
In addition, entity B has a many-to-many relation with an entity C.
When I first store a transient object of type A, both A and related
transient B entity instances associated with A are correctly created in
the database, but transient C instances associated with B aren't created.
The many-to-many association is mapped in both sides of the association as
follows (mapping-by-code approach):
// Mapping for collection of Entity C on Entity B
@class.Set
(
entityB => entityB.EntityCList,
map =>
{
map.Table("EntitiesBInEntitiesC");
map.Cascade(Cascade.All);
map.Key(key => key.Column("EntityBId"));
map.Inverse(false);
},
map => map.ManyToMany(relMap => relMap.Column("EntityCId"))
);
// Mapping for collection of Entity B on Entity C
@class.Set
(
entityB => entityB.EntityBList,
map =>
{
map.Table("EntitiesBInEntitiesC");
map.Cascade(Cascade.All);
map.Key(key => key.Column("EntityCId"));
map.Inverse(false);
},
map => map.ManyToMany(relMap => relMap.Column("EntityBId"))
);
Also, when entity B and entity C is instantiated when they're both
transient objects yet, I add the one of entity B on the collection of
entity C and viceversa.
Finally, the transaction ends successfully: I mean that the entity A and
B, and their association are stored in the database as expected.
Why the entity C associations aren't persisted in the database? What am I
doing wrong?
NOTE: I'm using the latest version of NHibernate 3.x series.