why hotspot users log with 2 ips ( address , to address ) ?

hello ,
I’m using MT 3.3

  • I assigned to user X ip #12 in the DHCP leases
  • made him a user ( IP - users ) & put the ip #12 in it
  • after X logs in , in the Hosts menu I found 2 IPs , ( the one I assigned in “Address” & a new random Ip in “To address” )

why is that ?
& how could I adjust it to become the same Ip in “Address” & “to address” ?