From Jason Howlett, using suggestion from Robert Osfield, "CullVisitor.cpp was modified, beginning at line 1115. Code was added to

check if the camera inherits its cull mask. If not, the CullVisitor sets
its traversal mask to the camera's cull mask."

src/osgUtil/CullVisitor.cpp

@@ -1112,6 +1112,14 @@ void CullVisitor::apply(osg::Camera& camera)
     // activate all active cull settings from this Camera
     inheritCullSettings(camera);
 
+    bool hasSetCullMask =
+        (camera.getInheritanceMask() & osg::CullSettings::CULL_MASK) == 0;
+
+    if (hasSetCullMask)
+    {
+        setTraversalMask(camera.getCullMask());
+    }
+
     RefMatrix& originalModelView = *getModelViewMatrix();
 
     osg::RefMatrix* projection = 0;