Rather than go to hoops to kill states of an iface and still seem even with FreeBSD 9 changes will be stack on not if-bound states simplify code on pf for state tracking, which might improve a bit performance as well to always do operation for states on the all anchor interface. Though store the interface where the state originated from so that pfctl -i -k[K] can work its magic on killing states for an interface
Make the BOUND_IFACE correct. This should solve the issues with handling ftp on other wans than default gateway