pfSense

If you have an interface with an IP type of "none", and then create a port forward on that interface with a destination of "any", it leads to an invalid ruleset.

Config snip of the offending port forward:

                <rule>
                        <source>
                                <any/>
                        </source>
                        <destination>
                                <any/>
                                <port>80</port>
                        </destination>
                        <protocol>tcp</protocol>
                        <target>192.168.1.55</target>
                        <local-port>80</local-port>
                        <interface>opt1</interface>
                        <descr/>
                        <associated-rule-id>nat_4e738285d7c807.89552620</associated-rule-id>
                        <value>default</value>
                </rule>

Leads to these rules:

rdr on vr2 proto tcp from any to any port 80 -> 192.168.1.55
no nat on vr2 proto tcp from (vr2) to /
nat on vr2 proto tcp from / to 192.168.1.55 port 80 -> (vr2)