I have DHCP enabled on my LAN interface, OPT1 and OPT3 (the latter a wireless interface).
DHCP assigns addresses from the correct range on all these interfaces.
I'm running pfSense 1.2.3-RC2 built on Tue Jun 16 04:58:42 EDT 2009
What version are you running?
On my pfSense box the dhcpd configuration file (/var/dhcpd/etc/dhcpd.conf) specifies addresses based on subnets rather than interfaces so, if your box follows the same pattern, its hard to see how dhcpd could get confused as to which addresses apply to which interface.
Do you have any static DHCP assignments? (Possible duplicated static assignments?)
Have you checked that the DHCP address assignments are actually made by the server you expect?