Not sure this is intentionally, but that was not the case in 7.40x, seems if a node is syncing we still can click on reboot/shutdown for it, and it is doing it immediatly !
You should not be able to reboot the Master while the Slave is in state SYNCING.
However you are able to reboot Slave/Worker nodes while they are in state SYNCING. There is nothing wrong about that, the nodes will restart the synchronization process after the system restart.
You should not be able to reboot the Master while the Slave is in state SYNCING.
However you are able to reboot Slave/Worker nodes while they are in state SYNCING. There is nothing wrong about that, the nodes will restart the synchronization process after the system restart.