delegate mouse press event if selected item is not a typed node

sketchUI/exm_scene.py

@@ -70,6 +70,8 @@ class SketchScene(QGraphicsScene):
             # load attributes for selected item (if it is a typed node)
             item = self.itemAt(event.scenePos(), QTransform())
             if not item or not isinstance(item, GraphicsNodeItem):
+                # just a sketched element, delegate event
+                QGraphicsScene.mousePressEvent(self, event)
                 return
 
             self._parent.tableWidget.setRowCount(0)