R8000P / Advanced / Setup / Lan Setup / Address Reservation

R8000P / Advanced / Setup / Lan Setup / Address Reservation:  

I am trying to add devices to the Address Reservation List.  When I click [Add] - it gives me a list of all attached devices - 

then I select the device I want to Reserve Address for - 

at this point the current info for the device is populated at the bottom of the screen - this is where I modify the 'Current Address' to the address I want to be reserved for this device - an I get and "Invalid MAC Address" error for that MAC address.  

I have double checked to verify the address i am wanting to reserve is not already reserved, nor is it already assigned to any devices.  

I have done this procedure in the past - but I believe my problem may be with an updated firmware which is "V1.4.4.94_1.3.56" .  

Is  there a way to make this work.  Going into the Device via putty/etc is NOT an option for this device.  My Address Reservation MUST be via Router.