Hi Adele,

The issue stems from the ListCollectionView actually.  When you change the Product value this causes the ListCollectionView's CanAddNew property to become false because there is currently an edit transaction occurring.  In the middle of this edit transaction, LoadCustomizations() is being called and during this process the AddNewRecord get's removed because the grid thinks ListCollectionView doesn't allow new items (because CanAddNew is false).  To resolve this you need to end the edit transaction before calling LoadCustomizations.

In your behavior change the LoadLayout method to look like this:

protected  void LoadLayout(string fileName)
{
	Application.Current.Dispatcher.BeginInvoke(new Action(() =>
	{
		try
		{
			var path = System.IO.Path.Combine(LayoutPath, fileName);
			if (System.IO.File.Exists(path))
				using (var file = System.IO.File.OpenRead(path))
				{
					AssociatedObject.ExecuteCommand(DataPresenterCommands.EndEditModeAndCommitRecord);
					AssociatedObject.LoadCustomizations(file);
				}
		}
		catch (Exception ex)
		{
			Debug.WriteLine("Error loading layout {0}", ex.Message);
		}
	}));
}

The BeginInvoke is required because you can't end edit mode in the grid in the middle of the Product property changed event which the behavior is currently doing.  This BeginInvoke allows the grid to react properly when you execute the EndEditModeAndCommitRecord command.