Use attached to reproduce.
Workaround:
private void RadDiagram1_ItemsChanged(object sender, Telerik.WinControls.UI.Diagrams.DiagramItemsChangedEventArgs e){ if (e.Action == System.Collections.Specialized.NotifyCollectionChangedAction.Add) { IEditableObject editableObject = ((RadDiagramShape)e.NewItems.First()).DataBoundItem as IEditableObject; if (editableObject != null) { editableObject.EndEdit(); } }}