dnsmasq DHCP server doesn't release a leased IP address.

Issue

• On the customer's system, OpenStack(Essex) executes dnsmasq service to provide DHCP service for the virtual guests.
• Many dnsmasq processes are started with each --dhcp-hostsfile option for each virtual network.
• When a virtual machine is created or deleted, OpenStack modifies the corresponding dhcp-hostsfile (e.g. /var/lib/nova/networks/nova-br1207.conf) and executes dhcp_release command to release the leased IP address the old virtual machine used.
• /var/lib/nova/networks/nova-br1207.conf

fa:16:3e:54:9e:2c,11.novalocal,10.192.6.3
fa:16:3e:66:41:5b,111.novalocal,10.192.6.4
fa:16:3e:24:2c:6c,1.novalocal,10.192.6.8

• But it seems that dnsmasq DHCP server don't release the old IP address. As a result, it can't lease a IP address for a new virtual machine.
• /var/log/messages-20121202.gz

Nov 28 14:37:54 xxxxxx dnsmasq-dhcp[31445]: 550177792 Available DHCP subnet: 10.192.6.3/255.255.255.192
Nov 28 14:37:54 xxxxxx dnsmasq-dhcp[31445]: not using configured address 10.192.6.3 because it is leased to fa:16:3e:65:bb:4f
Nov 28 14:37:54 xxxxxx dnsmasq-dhcp[31445]: 550177792 DHCPDISCOVER(br1207) 10.0.2.15 fa:16:3e:54:9e:2c no address available

• He says that he tried a dnsmasq of the community (version 2.63) and it can lease one correctly, but dnsmasq-2.48-7.el6.x86_64.rpm on RHEL6 Beta Channel doesn't work well.