dhcp question/problem

[RJ45]

Hello, I am using a dhcp server on FreeBSD.
I have a strange problem.
I defined in my dhcpd.conf 2 subnets for dhcp. 
My problem is that IP addresses are assigned always
from subnet 172.16.250.0 even if the MAC address
requesting the address (IDEFIX) is written in the 172.16.254.0 entry,
and gateway assigned instead is the one from subnet 172.16.254.0.
I mean it's like if dhcpd ignores subnet 172.16.254.0 after I Added
new subnet  172.16.250.0

How can  I solve this problem? using fixed-address I Can solve it but
I do not want to use fixed-address.
here is my congfiguration below

shared-network fi {

   option domain-name-servers   192.84.x.y, 193.206.x.y;
   option domain-name           "mydomain.it";
   option subnet-mask           255.255.255.0;

   deny unknown-clients;

    subnet 172.16.254.0 netmask 255.255.255.0 {
      range                     172.16.254.1 172.16.254.150;
      default-lease-time        43200;
      max-lease-time            86400;
      option routers            172.16.254.254;
      option broadcast-address  172.16.254.255;

      deny unknown-clients;
      host IDEFIX { 
         hardware ethernet 08:00:46:69:d7:19; 
      } 
        etc.... other hosts follow
    }
 subnet 172.16.250.0 netmask 255.255.255.0 {
      range                     172.16.250.1 172.16.250.250;
      default-lease-time        43200;
      max-lease-time            86400;
      option routers            172.16.254.254;
      option broadcast-address  172.16.254.255;

      deny unknown-clients;

      host IDEFIX2 {
         hardware ethernet 00:50:56:40:00:7F;
      }
        etc... other hosts follow
    }
}


thanks a lot

Rick