I discovered today that if you have created your interfaces on a CARP Backup pfSense firewall "in a different order than your primary firewall", than during XMLRPC syncronization I had two interfaces updated with another interface's rules. The syncing even stopped after the SYNC interface rules on the Backup firewall were replaced with WAN2 rules.
I am using 2.0-RC1 (i386) built Mar 3 02:31:32 EST 2011 on both firewalls. I have 5 NIC's assigned as WAN1, LAN, WAN2, SYNC, WLAN on both firewalls.
Initially I could see the list of interface name tabs at the top of the Dashboard -> Firewall Rules were in a different order between Master and Backup firewalls. At a hunch, I reversed the effected two physical interface NICs, Interface Names and IP/masks and applied the settings, repaired the wrong rule for SYNC interface and syncronization worked perfectly and the correct rules per interface were updated on the backup firewall. A pair of happy pfSense pups !
I expect there must be some stray hard coding linking the original OPT1, 2, 3 interface assignment rather than the user assigned Interface named ?
Again, many thanks guys for a brilliant tool !