Implement a user-friendly way to select (and, for example, eventually delete) "orphaned" items in the model explorer (by "orphaned" I mean items that have been deleted from the diagram, but not from the model).

Here is a use case: When I delete a Flow in an Activity diagram from the diagram (but not from the model), the Flow will persist in the model. Now I understand that there might be times when this is useful, but since I could not find a way to drag it back to the diagram, I consider it lost anyway (but maybe I'm missing something out here). Consequently, cleaning up such items -- particularly in early model drafting phases -- can be tedious at times, in particular if it has to be done item by item (checking if its orphaned, or not).