diff --git a/typetapper/hierarchy_graph.py b/typetapper/hierarchy_graph.py
index df3dfea..cd53ba1 100644
--- a/typetapper/hierarchy_graph.py
+++ b/typetapper/hierarchy_graph.py
@@ -139,10 +139,11 @@ class HierarchicalGraph(RelativeAtomGraph):
 
     def _add_node(self, relatom: RelativeAtom, path: OpSequence, has_gone_down: bool) -> bool:
         res = super()._add_node(relatom, path, has_gone_down)
-        if res:
+        if relatom not in self.__graph.nodes:
             self._atom_parents[relatom] = self._current_group
             self._current_group.children.add(relatom)
             self.__graph.add_node(relatom)
+        if res:
             self._prop_propagate(relatom, True)
         self.check_invariants()
         return res
diff --git a/typetapper/hierarchy_graph_view.py b/typetapper/hierarchy_graph_view.py
index 0891e17..48c28c1 100644
--- a/typetapper/hierarchy_graph_view.py
+++ b/typetapper/hierarchy_graph_view.py
@@ -671,7 +671,7 @@ class HierarchicalGraphWidget(QZoomableDraggableGraphicsView):
 
     def mousePressEvent(self, event):
         self._mouse_is_down = True
-        if event.modifiers() & Qt.ShiftModifier == 0:
+        if (event.modifiers() & Qt.ShiftModifier) == Qt.NoModifier:
             self.setDragMode(QZoomableDraggableGraphicsView.ScrollHandDrag)
         else:
             self.setDragMode(QZoomableDraggableGraphicsView.RubberBandDrag)
@@ -781,7 +781,7 @@ class HGNode(AnimatableItem):
 
     def exit(self, duration=250):
         self.exiting = True
-        for edge in self.edges.values():
+        for edge in list(self.edges.values()):
             edge.orient(self, away=True)
             edge.exit(duration)
             edge.start.edges.pop(self.model, None)
diff --git a/typetapper/relative_graph.py b/typetapper/relative_graph.py
index cb57ad7..6ee238e 100644
--- a/typetapper/relative_graph.py
+++ b/typetapper/relative_graph.py
@@ -57,7 +57,6 @@ class RelativeAtomGraph:
         If relatom is not present in the graph, add it.
         If it is present in the graph, merge the new information into its attrs
         """
-        from .data import RegisterAtom
         newattrs = RelativeAtomAttrs(
             prop=self.kp.graph.nodes[relatom.atom].get('prop', Prop()).transform(path.invert()),
             path=path,
@@ -116,9 +115,6 @@ class RelativeAtomGraph:
             edge_ops: OpSequence,
             is_pred: bool,
     ) -> Optional[RelativeAtom]:
-        #if str(relatom.atom) == 'rsp @ 0x4144a8' and str(succ) == 'MEM @ 0x4144d9':
-        #    import ipdb; ipdb.set_trace()
-
         weh = self._update_callstack(relatom.callstack, relatom.rcallstack, edge_cf, is_pred)
         if weh is None:
             return None