src/Pure/Thy/sessions.scala

     imports: Option[Base] = None)
   {
     def platform_path: Base = copy(known = known.platform_path)
     def standard_path: Base = copy(known = known.standard_path)
 
+    def theory_qualifier(name: Document.Node.Name): String =
+      global_theories.getOrElse(name.theory, Long_Name.qualifier(name.theory))
+
     def loaded_theory(name: String): Boolean = loaded_theories.defined(name)
     def loaded_theory(name: Document.Node.Name): Boolean = loaded_theory(name.theory)
 
     def loaded_theory_syntax(name: String): Option[Outer_Syntax] =
       if (loaded_theory(name)) Some(loaded_theories.get_node(name)) else None

               def session_node(name: String): Graph_Display.Node =
                 Graph_Display.Node("[" + name + "]", "session." + name)
 
               def node(name: Document.Node.Name): Graph_Display.Node =
               {
-                val qualifier = resources.theory_qualifier(name)
+                val qualifier = imports_base.theory_qualifier(name)
                 if (qualifier == info.name)
                   Graph_Display.Node(name.theory_base_name, "theory." + name.theory)
                 else session_node(qualifier)
               }