JPAContainer not loading ManyToMany

Hello,
I have two model classes A and B with a @manytomany relationship.
I have made a Vaadin crud application.
When I persist the relationships from A to B are persisted.
When I then load the the same item from A using jpacontainer getItem() it has an empty set so it has lost relationships to B.
The most incredible thing is that if I go in to db JUST AFTER getItem() JPAContainer has already deleted the relationships in the relation table. I have just READ the item, not yet written it or commit().
Can you help me?
Thanks,
Mario

Update: apparently setting the item as a FieldGroup datasource mangle it.
I suppose because I have binded all fields but the manytomany one.
I cannot bind the manytomany field because of a ClassCast exception (bug…) in MultiSelectConverter.
I ask again: is someone is really using Vaadin7 to develop applications?
Because I am seeing that FieldGroups with JPAContainer have many problems. They works only in simple use cases like modifying (and not adding) a simple entity with no relationships.
And I see tickets open for MultiSelectConverter interaction with FieldGroup more than one year ago and not yet considered.

I do not understand…

Mario

Update: problem solved.
In twincolselect I must use setValue() before setPropertyDataSource() but even now I have solved it I am worried that data on DB should be committed when I call commit() on container and not before.

A couple of years ago I abandoned JPAContainer because of these kind of problems… Now, I’m starting a new application and I’ll try again.

¿Have you tried using BeanFieldGroup?