The patch to add the bridgein built-in rule to ipchains makes the "delete all chains" command, ipchains -X, issue the following error:
ipchains: Device or resource busy
As far as I can tell this is harmless. I suspect that ipchains does not understand that the new bridgein rule is a builtin.
As I mentioned in Hardware Setup, at least for PCI NIC's you do not want to share interrupts between the two cards (or probably with any other device).