pfSense

If I make a static DHCP mapping configuration where leave the IP address box blank (I want the IP given out to be dynamically allocated from my pool), the static lease is ignored by the DHCP server. When a client with a matching MAC address connects to the network, the static mapping I've made is ignored and the DHCP server generates a new one just like I hadn't ever configured the static mapping. Filling in the IP Address field causes the DHCP server to respect my static mapping configuration.

The static DHCP mapping UI for the IP Address entry box says:

"Address must be outside of any defined pools. If no IPv4 address is given, one will be dynamically allocated from a pool.
The same IP address may be assigned to multiple mappings."