src/Pure/PIDE/markup.scala

   val BUILD_THEORIES_RESULT = "build_theories_result"
   object Build_Theories_Result
   {
     def unapply(props: Properties.T): Option[String] =
       props match {
-        case List((FUNCTION, BUILD_THEORIES_RESULT), ("id", id)) => Some(id)
+        case List((FUNCTION, BUILD_THEORIES_RESULT), (ID, id)) => Some(id)
         case _ => None
       }
   }
 
   val PRINT_OPERATIONS = "print_operations"