dhcpd.leases set ddns

[Andreas Moroder]

Hello,

when certain printers ask for a new lease the lease files contains lines 
of like the following

   set ddns-fwd-name = "ps-int-sek.sb-brixen.it";
   set ddns-rev-name = "252.5.53.10.in-addr.arpa.";
   on expiry or release {
     switch (ns-update (delete (1, 12, ddns-rev-name, null))) {
      case 0:
       unset ddns-rev-name ;
       break;
     }
     switch (ns-update (delete (1, 1, ddns-fwd-name, leased-address))) {
      case 0:
       unset ddns-fwd-name ;
       break;
     }
     on expiry or release;
   }


For other printer there are no such lines in the lease file.

Can anyone please tell me what's the reason for this difference ?
We have a 3.0.4 dhcpd. I know it is old and we plan to switch in the 
next days.

Thanks
Andreas