From Lionel Lagarde, "The copy constructor of the nodes and the drawables do :

Node::Node(Node &node, copyop) :
  _stateSet(copyop(node.getStateSet()),

It doesn't call the setStateSet method of osg::Node (or osg::Drawable). So the parent
list of the state set is not updated with the new node (drawable)."

src/osg/Drawable.cpp

@@ -223,7 +223,6 @@ Drawable::Drawable()
 Drawable::Drawable(const Drawable& drawable,const CopyOp& copyop):
     Object(drawable,copyop),
     _parents(), // leave empty as parentList is managed by Geode
-    _stateset(copyop(drawable._stateset.get())),
     _initialBound(drawable._initialBound),
     _computeBoundCallback(drawable._computeBoundCallback),
     _boundingBox(drawable._boundingBox),
@@ -240,6 +239,7 @@ Drawable::Drawable(const Drawable& drawable,const CopyOp& copyop):
     _cullCallback(drawable._cullCallback),
     _drawCallback(drawable._drawCallback)
 {
+    setStateSet(copyop(drawable._stateset.get()));
 }
 
 Drawable::~Drawable()

src/osg/Node.cpp

@@ -82,9 +82,9 @@ Node::Node(const Node& node,const CopyOp& copyop):
         _numChildrenWithCullingDisabled(0), // assume no children yet.
         _numChildrenWithOccluderNodes(0),
         _nodeMask(node._nodeMask), 
-        _descriptions(node._descriptions),
-        _stateset(copyop(node._stateset.get()))
+        _descriptions(node._descriptions)
 {
+    setStateSet(copyop(node._stateset.get()));
 }
 
 Node::~Node()