DHCP-Server + radius + add arp

Dear colleauges,

I have such scheme:
Mikrotik with dhcp server communicates with radius server (freeradius 3). It works fine. But, when I turned on an option add arp in dhcp server settings - it does not work. Is it bug or feature?

Hi Gutzeit
As far as i know the option add arp is not a predefined function in DHCP-SERVER RFC
Maybe it could explain why is not working whith freeradius.