Strange behaviour wit 1:n collection with EJB 3.0 and Tomcat

[statelessbean]

Hi,
Can anyone explain me what is going one?
I got collection mapped (one directional) from planet->buildingsProd class like this

@OrderBy("index ASC")
@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.LAZY)
@JoinColumn(name="Planet_idPlanet")
public List<BuildingsProd> getBuildingsProdList() {
 if (buildingsProdList == null)
 buildingsProdList = new LinkedList<BuildingsProd>();
 return buildingsProdList;

and when I load my planet

Planet planet = em.find(Planet.class, idPlanet);

and add new object to collection

BuildingsProd b = new BuildingsProd();
planet.getBuildingsProdList().add(b);
em.merge(planet);

new object should me inserted into db with my planet key and here is my question.
This works fine on JBoss 4.0.5 but on tomcat with jboss embedded new object is inserted into db but withoud planet FK key!!!
Why, and what is wrong here?

I got also installed JBoss embedded for my tomcat and seam 2.0.0 CR 2 app.