Jennifer,
I'm not editing points but I am trying to union point selections when the user chooses "add to selection" in my application. The union operation doesn't seem to work for multipoint features which sounds kind of like what you were talking about here. But like I said, im not editing points. Can you verify that points cannot be "unioned" to multi point features? When the user chooses "New Selection" and selects several points, all the individual point features seem to union into one multipoint feature fine. It's just this "Add to Selection" and the operation of merging point(s) with multipoints that doesn't work for me. Your help is appreciated. 🙂
Gary