I would try to ping the abandoned leases. An abandoned lease is a lease that the DHCP server tries to assign, but it responds to a ping. http://linux.die.net/man/5/dhcpd.conf
Your scope does not leave you enough flexibility if a devices with static ip addresses takes your leases away from you. If you only have access points on that subnet, you should 1. Clear all of your ip address bindings, (2) reboot all of your access points and see what leases get re-used
1. clear ip dhcp binding
2. apboot all local