protected override bool ExecuteSave()
        {
            var entities = this.EntityManager
                    .FindEntities(EntityState.Modified)
                    .OfType<Entity>()
                    .ToList();
 
            foreach (var entity in entities)
            {
                var key = (int) entity.EntityAspect.EntityKey.Values[0];
 
                if (key < 0)
                    entity.EntityAspect.SetAdded();
            }
 
            return base.ExecuteSave();
        }

If I take out the accept/set modified code, when I merge the additions from one EM into another it duplicates. 

Has there been any progress on resolving these issues?

            OriginalManager.FindEntities<Entity>(EntityState.Added)
                .ForEach(e =>
                                 {
                                     e.EntityAspect.AcceptChanges();
                                     e.EntityAspect.SetModified();
                                 });
 
            var restoreStrategy = new RestoreStrategy(false, false, MergeStrategy.OverwriteChanges);
            var data = repositoryBase.Manager.CacheStateManager.GetCacheState();
            NewManager.CacheStateManager.RestoreCacheState(data, restoreStrategy);
 
            var entities = Manager.FindEntities<Entity>(EntityState.Modified)
                .Where(e => (int)e.EntityAspect.EntityKey.Values[0] < 0).ToList();
 
            entities.ForEach(e => e.EntityAspect.SetAdded());


To stop the new manager from assigning a new Id, I have to call AcceptChanges and then SetModified.

Since I am using integer primary keys, I can find the true "Added" entities by finding the ones with a negative key. I then set these back to Added in the new manager.
Also, to get around duplicating the same negative key, I have had to alter the default ID generator. It now uses a static _nextId variable so that all instances use the same id counter.

This seems to work, the only issue is on saving where even though they are set to added, they get duplicated in the EM after saving, the original Added entities, and the new saved unchanged entities.

I have had to do this to get around it:

        private void OnSaveSuccess()
        {
            var addedEntities = Manager.FindEntities(EntityState.Added)
                .OfType<Entity>()
                .ToList();
 
            for (var i = addedEntities.Count-1; i >= 0; i--)
            {
                addedEntities.EntityAspect.Delete();
            }
        }

If there is a better/cleaner way of doing this, I'm all ears.