My RB3011 reboots within 30 seconds after trying to shutdown it from Winbox
Yes, all RouterBOARDs will do this, it is not a bug per-se, it is more something like unsupported feature. Device needs to be disconnected from power to turn off completely. If you don’t unplug it, it will start again. Shutdown command is not required, it is quite safe to just unplug it.