Strange DHCP behaviour

[tony]

Hi,
I'm running a DHCP server (4.3) under Debian Stretch to serve a small
local domain. It behaves well for most clients, but I have a laptop
(also Debian Stretch) for which I wish to assign a fixed address. My
server configuration is this (tony-lt being the laptop):
------------------------------------------------------------------
# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;

# option definitions common to all supported networks...
#option domain-name "example.org";
option domain-name "chalet.vanderhoff.org";
#option domain-name-servers ns1.example.org, ns2.example.org;
option domain-name-servers 192.168.1.1;

default-lease-time 600;
max-lease-time 7200;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.

#subnet 10.152.187.0 netmask 255.255.255.0 {
#}

# This is a very basic subnet declaration.

subnet 192.168.1.0 netmask 255.255.255.0
{
        range 192.168.1.200 192.168.1.254;
        option routers 192.168.1.10;
}

host tony-lt
{
        hardware ethernet 0c:60:76:6c:e6:6f;
        fixed-address 192.168.1.199;
}
------------------------------------------------------------------

Despite this configuration I have failed to get that address for the
laptop; it seems to be stuck on 192.168.1.254, currently. It may have
legitimately had that address in the past.

I have stopped and cleared the client via 'dhclient -r', deleted the
files in /var/lib/dhclient, before restarting it with 'dhclient -v, It
immediately requests ..254

I'm seeing this in the server log:
------------------------------------------------------------------
Oct 24 12:52:04 router-pi dhcpd[1068]: DHCPREQUEST for 192.168.1.254
from 0c:60:76:6c:e6:6f (tony-lt) via eth0
Oct 24 12:52:04 router-pi dhcpd[1068]: DHCPACK on 192.168.1.254 to
0c:60:76:6c:e6:6f via eth0
Oct 24 12:52:24 router-pi dhcpd[1068]: DHCPREQUEST for 192.168.1.244
from f4:81:39:82:53:c4 via eth0
Oct 24 12:52:24 router-pi dhcpd[1068]: DHCPACK on 192.168.1.244 to
f4:81:39:82:53:c4 via eth0
Oct 24 12:52:32 router-pi dhcpd[1068]: DHCPREQUEST for 192.168.1.254
from 0c:60:76:6c:e6:6f via eth0
Oct 24 12:52:32 router-pi dhcpd[1068]: DHCPACK on 192.168.1.254 to
0c:60:76:6c:e6:6f (tony-lt) via eth0
Oct 24 12:52:41 router-pi dhcpd[1068]: reuse_lease: lease age 9 (secs)
under 25% threshold, reply with unaltered, existing lease for 192.168.1.254
Oct 24 12:52:41 router-pi dhcpd[1068]: DHCPREQUEST for 192.168.1.254
from 0c:60:76:6c:e6:6f (tony-lt) via eth0
Oct 24 12:52:41 router-pi dhcpd[1068]: DHCPACK on 192.168.1.254 to
0c:60:76:6c:e6:6f (tony-lt) via eth0
------------------------------------------------------------------

Apart from the rather frequent lease request, which I suspect is due to
NetworkManager on this laptop, what is the 'reuse-lease' comment?

Has anyone any suggestions on how to fix this, please?

Cheers, Tony