Unable to change Device Name (or rename) using Access Control - R6900P

I have been trying to fix some device names under access control in my R6900P router. It takes the change, I apply it on the edit screen as well as in the "allowed devices" screen but then when I refresh the screen it remains as it was before my edit. 

Please suggest a way to make the name change remain in place. 

Note in some cases the name is 

'---'

whereas in other cases it has an alpha numeric string.

Thanks

Chris