It is not passible to add a (sub)network to firewall groups that is in use by IPsec or OpenVPN (error: The given subnet address is already used by an IPsec network...). So it is not possible to create group-based firewall rules to filter tunnel traffic (e.g. if the tunnel endpoint's subnet is a /16 private network but structered into /24 networks with different firewall policies). This is caused by checksubnets($fwhostsettings{'HOSTNAME'},$fullip,""); (/srv/web/ipfire/cgi-bin/fwhosts.cgi:304).
*** This bug has been marked as a duplicate of bug 11131 ***