Strange behaviror : duplicated entities when using sand box editors

Hi !,
I have a strange behavior,
I 'm using sandbox editors to edit/add an entity,
I have a main entity manager, and an entity manager used to edit/add entities
When I create new entity, (using the sandbox EM), and import it to the main EM, there is no problem.
then I try to edit the newly created entity (which is not commited to Database) , in a new sandBox EM, and import it again
in the main EM, there is 2 new entities !!!

see the code below (I used linqpad, My model is named GeDoseEntities)

void Main()
{

    var em1 = new GedoseEntities(); //main Entity Manager
   
   
   
    // 1st editor
    var em2 = new GedoseEntities(); //this EM will create the entity
    var newsite = new Site() { Nom="service d", OrganismeId = 1};
    em2.AddEntity(newsite);
   
    //1st edition : creation
    bool validateCreation = true;
   
    if(validateCreation)
    {
        var entities = em2.FindEntities(IdeaBlade.EntityModel.EntityState.AnyAddedModifiedOrDeleted);
        em1.ImportEntities(entities,MergeStrategy.OverwriteChanges);   
   
    }
    else
    {
        em2.Clear();
        return;
    }
   
    // at this point the newly crated entity is imported to the main EM , and there is only one instance
   
    // dump into linqpad outut
    em1.FindEntities(IdeaBlade.EntityModel.EntityState.AnyAddedModifiedOrDeleted).Dump("after creation");   
   
   
    // edit the newlyt created entity (!! : not commited to the database)
    int id = newsite.Id;   
    var siteToEdit = em1.Sites.FirstOrDefault(s=>s.Id==id);
   
    // EM used to edit the entity
    var em3 = new GedoseEntities();       
    var entitiesToimport = em1.FindEntities(IdeaBlade.EntityModel.EntityState.AnyAddedModifiedOrDeleted);
    em3.ImportEntities(entitiesToimport,MergeStrategy.OverwriteChanges);   
    em3.FindEntities(IdeaBlade.EntityModel.EntityState.AllButDetached).Dump("e3");   
   
    {
        var siteToModify = em3.Sites.FirstOrDefault(s=>s.Id==id);   
   
        // modif
        siteToModify.Nom += "+++";   
        siteToEdit.Dump("site to edit");
        siteToModify.Dump("site to modify");   
    }
   
   
    bool validateModification = true;
   
    if(validateModification)
    {       
        var entities = em3.FindEntities(IdeaBlade.EntityModel.EntityState.AnyAddedModifiedOrDeleted);           
        em1.ImportEntities(entities,MergeStrategy.OverwriteChanges);   
    }
    else
    {
        em3.Clear();
    }
   
    em1.FindEntities(IdeaBlade.EntityModel.EntityState.AnyAddedModifiedOrDeleted).Dump("To update");
    // at this point there is two new entities !!!
   
}


Thanks