DHCP Server on Intrface only deploys 1 DNS IP to clients

Hi

Is it a bug or did we something wrong? On a FW60D with 5.6.3 we have the DHCP server configured on the Internal Interface with 3 DNS servers, but on the clients we just always get 1 DNS IP.

config system dhcp server
    edit 1
        set lease-time 43200
        set forticlient-on-net-status disable
        set ntp-service default
        set default-gateway 192.168.5.1
        set netmask 255.255.255.0
        set interface "internal"
        config ip-range
            edit 1
                set start-ip 192.168.5.100
                set end-ip 192.168.5.250
            next
        end
        set timezone-option default
        set dns-server1 192.168.5.1
        set dns-server2 172.17.36.60
        set dns-server3 8.8.8.8
    next

But on all Win Clients we get only the primary DNS, dns-server1 with the value "192.168.5.1".

Scheda Ethernet Connessione alla rete locale (LAN):

   Suffisso DNS specifico per connessione:
   Descrizione . . . . . . . . . . . . . : Realtek PCIe GBE Family Controller
   Indirizzo fisico. . . . . . . . . . . : 6C-62-6D-EF-7E-10
   DHCP abilitato. . . . . . . . . . . . : Sì
   Configurazione automatica abilitata : Sì
   Indirizzo IPv6 locale rispetto al collegamento . : fe80::8ca9:2004:c6e4:507%1
2(Preferenziale)
   Indirizzo IPv4. . . . . . . . . . . . : 192.168.5.132(Preferenziale)
   Subnet mask . . . . . . . . . . . . . : 255.255.255.0
   Lease ottenuto. . . . . . . . . . . . : lunedì 7 maggio 2018 09:37:34
   Scadenza lease . . . . . . . . . . . : lunedì 7 maggio 2018 21:37:32
   Gateway predefinito . . . . . . . . . : 192.168.5.1
   Server DHCP . . . . . . . . . . . . . : 192.168.5.1
   IAID DHCPv6 . . . . . . . . . . . : 275538541
   DUID Client DHCPv6. . . . . . . . : 00-01-00-01-1A-C2-3C-EE-6C-62-6D-EF-7E-10

   Server DNS . . . . . . . . . . . . . : 192.168.5.1
   NetBIOS su TCP/IP . . . . . . . . . . : Attivato

Does anyone know why dns-server2 and dns-server3 values never reach the clients?

Thanks