JPA/Hibernate inheritance while loading: IllegalArgumentException, try to set wrong subclass - jpa

Question

I'm using JBoss 6.1, I have the a JPA entagled situation, as a result I got the following error message:
IllegalArgumentException: Can not set EquipmentB field EquipmentCycleB.equipment to EquipmentA
suppose that each entity has an #Id annotated field:
A first hierarchy
#Entity
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
#DiscriminatorColumn(name = "DIS", discriminatorType = DiscriminatorType.STRING, length = 1)
public abstract class Equipment { ... }
#Entity
#DiscriminatorValue("A")
public class EquipmentA extends Equipment { ... }
#Entity
#DiscriminatorValue("B")
public class EquipmentB extends Equipment { ... }
A second hierarchy
#Entity
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
#DiscriminatorColumn(name = "DIS", discriminatorType = DiscriminatorType.STRING, length = 10)
public abstract class EquipmentCycle {
...
}
#Entity
#DiscriminatorValue("A")
public class EquipmentCycleA extends EquipmentCycle {
#JoinColumn(name = "EQUIPMENT_ID", referencedColumnName = "ID")
#ManyToOne
private EquipmentA equipment;
...
}
#Entity
#DiscriminatorValue("B")
public class EquipmentCycleB extends EquipmentCycle {
#JoinColumn(name = "EQUIPMENT_ID", referencedColumnName = "ID")
#ManyToOne
private EquipmentB equipment;
...
}
So far nothing strange, go on, the class say Status
#Entity
public class State {
#JoinColumn(name = "ENTITY_ID", referencedColumnName = "ID", nullable = false)
#ManyToOne
private EnityWithState enityWithState;
#JoinColumn(name = "EQUIPMENT_ID", referencedColumnName = "ID")
#ManyToOne
private Equipment equipment;
#JoinColumn(name = "EQUIPMENT_CYCLE_ID", referencedColumnName = "ID")
#ManyToOne
private EquipmentCycle equipmentCycle;
...
}
and the class which the state belong to
public class EnityWithState {
...
#OneToMany(mappedBy = "enityWithState", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
private List<State> stateHistory;
...
}
Don't ask me why, I have just found it.
After some time the DB store the following data
Table Equipment
ID DIS
--------------------------------
1 A ...
2 B ...
Table EquipmentCycle
ID DIS EQUIPMENT_ID
--------------------------------
1 A 1
2 B 2
Table State
ID ENTITY_ID EQUIPMENT_ID EQUIPMENT_CYCLE_ID
---------------------------------------------
1 1 1 1
2 1 2 2
And finally, when I try lo load the EnityWithState with id 1, I got the following error:
IllegalArgumentException: Can not set EquipmentB field EquipmentCycleB.equipment to EquipmentA
Does anyone have any idea? I googled but I found nothing.
Could it be an Hibernate/JPA bug?
Thanks in advance for the help