anchor.diff:              end;
           {'$gc_unknown_event', NewState} -> NewState;
           {'$gc_exception', NewState} ->     NewState;
  +        unknown_event ->
  +            %% drop T2State, as it contains the error message
  +            TmpState = on_unknown_event(Msg, T1State),
  +            bp_step_done(Msg, TmpState);
           NewUState ->
               bp_step_done(Msg, gc_set_ustate(T1State, NewUState))
       end.
  
positive.code:             "~n** Exception:~n ~.0p:~.0p~n"
              "** Current message:~n ~.0p~n"
              "** Module:~n ~.0p~n"
              "** Source linetrace (enable in scalaris.hrl):~n ~.0p~n"
              "** State:~n ~.0p~n"
              "** Handler:~n ~.0p~n"
              "** Stacktrace:~n ~.0p~n",
              [Level, Reason,
               Msg,
               gc_mod(State),
               erlang:get(test_server_loc),
               State,
               gc_hand(State),
               Stacktrace]),
      State.
  
  
negative.code:                                  {"state", State}]}),
      State;
  on_unknown_event(UnknownMessage, State) ->
      log:log(error,
              "~n** Unknown message:~n ~.0p~n"
              "** Module:~n ~.0p~n"
              "** Handler:~n ~.0p~n"
              "** Pid:~n ~p ~.0p~n"
              "** State:~n ~.0p~n",
              [UnknownMessage,
               gc_mod(State),
               gc_hand(State),
               self(), pid_groups:group_and_name_of(self()),
               State]),
      State.
  
  on_exception(Msg, Level, Reason, Stacktrace, State) ->
  