src/Pure/PIDE/session.scala

           case Session.Dialog_Result(id, serial, result) if prover.defined =>
             prover.get.dialog_result(serial, result)
             handle_output(new Prover.Output(Protocol.Dialog_Result(id, serial, result)))
 
           case Protocol_Command(name, args) if prover.defined =>
-            prover.get.protocol_command(name, args:_*)
+            prover.get.protocol_command_args(name, args)
 
           case change: Session.Change if prover.defined =>
             val state = global_state.value
             if (!state.removing_versions && state.is_assigned(change.previous))
               handle_change(change)