diff --git a/cumulus/src/plugins/alpha/block/clocktree.py b/cumulus/src/plugins/alpha/block/clocktree.py
index acd19dfc..65abf42a 100644
--- a/cumulus/src/plugins/alpha/block/clocktree.py
+++ b/cumulus/src/plugins/alpha/block/clocktree.py
@@ -176,7 +176,8 @@ class ClockTree ( object ):
         quadTree           = self.spares.quadTree
         quadTree.bufferTag = self.clockNet.getName()
 
-        hyperClock = HyperNet.create( Occurrence(self.clockNet) )
-        for plugOccurrence in hyperClock.getTerminalNetlistPlugOccurrences():
-            quadTree.attachToLeaf( plugOccurrence )
-        quadTree.rsplitNetlist()
+        with UpdateSession():
+            hyperClock = HyperNet.create( Occurrence(self.clockNet) )
+            for plugOccurrence in hyperClock.getTerminalNetlistPlugOccurrences():
+                quadTree.attachToLeaf( plugOccurrence )
+            quadTree.rsplitNetlist()
diff --git a/cumulus/src/plugins/alpha/block/spares.py b/cumulus/src/plugins/alpha/block/spares.py
index 95d550fc..c03e2a5c 100644
--- a/cumulus/src/plugins/alpha/block/spares.py
+++ b/cumulus/src/plugins/alpha/block/spares.py
@@ -569,6 +569,8 @@ class Spares ( object ):
                                     % (topNet.getName(),headInstance.getName(),masterCell.getName()) )
             headPlug.setNet( topNet )
             self.addClonedCell( masterCell )
+        else:
+            masterNet = headPlug.getMasterNet()
         
         if tailPath.isEmpty(): return headPlug
         return self.raddTransNet( masterNet, tailPath )