Comment #4 on issue 650 by alexandr...@gmail.com: Mondrian multiple selection uses a broken metaphor http://code.google.com/p/moose-technology/issues/detail?id=650
Try the last version of Mondrian. I improved a bit the drag and drop. Unfortunately, the behavior that you describe is not easy to get in Morph :-( Give a try now, and if it does not work, and I will remove it.