message: Fix bug with Operation._control_inputs setter.
diff: @@ -2103,6 +2103,10 @@ class Operation(object):
  logging.warning("Operation._control_inputs is private, use "
  "Operation.control_inputs instead. "
  "Operation._control_inputs will eventually be removed.")
  + # Copy value because it may be self._control_inputs_val (in particular if
  + # this is called from self._control_inputs += ...), and we don't want to
  + # clear value below.
  + value = copy.copy(value)
  self._remove_all_control_inputs()
  self._add_control_inputs(value)
  