try to add shutdown handling

mission/devices/SyrlinksHandler.cpp

@@ -34,10 +34,15 @@ void SyrlinksHandler::doStartUp() {
 }
 
 void SyrlinksHandler::doShutDown() {
-  setMode(_MODE_POWER_DOWN);
+  // In any case, always disable TX first.
+  internalState = InternalState::SET_TX_STANDBY;
   commandExecuted = false;
-  internalState = InternalState::OFF;
+  if (commandExecuted) {
     temperatureSet.setValidity(false, true);
+    internalState = InternalState::OFF;
+    commandExecuted = false;
+    setMode(_MODE_POWER_DOWN);
+  }
 }
 
 ReturnValue_t SyrlinksHandler::buildNormalDeviceCommand(DeviceCommandId_t* id) {
@@ -798,7 +803,7 @@ void SyrlinksHandler::doTransition(Mode_t modeFrom, Submode_t subModeFrom) {
         commandDone();
       }
     }
-  } else {
-    commandDone();
+  } else if (tgtMode == HasModesIF::MODE_OFF) {
+    txStandbyHandler();
   }
 }