I've stumbled across an interesting problem recently:

• I've added a Linux box to my home network;
• It used my Cisco router to get a dynamic DHCP address;
• I've inspected the DHCP bindings on the Cisco router to find the new MAC address and configured a host DHCP pool as I'm using the Linux box as a server;
• Even after multiple configuration changes, the IOS would fail to use the host DHCP pool.

The only solution I've found was to restart the IOS DHCP server with the no service dhcp followed by service dhcp configuration commands. Obviously, you lose all DHCP bindings when you restart the DHCP server (which could be a problem if you use conflict logging) unless you've configured the router to store them in an external file.