pfSense

Example:
1) Start with a NAT port forward that has some special source type and destination type - e.g. just for fun source type LAN net, destination type This Firewall.
2) Edit the NAT port forward - change source type to Network, change destination type to Network. Do not actually input an network address.
3) Press Save
4) Input error messages are displayed (good):
The field Source address is required.
The field Destination address is required.
5) The source type remains as Network, awaiting entry of a network and mask - good.
6) The destination type becomes WAN address - problem!
If the user is not watching, they might end up leaving WAN address there because they do not realize what just happened.

I was expecting that it would either:
a) Redisplay the form with destination type Network, awaiting entry of the network and mask; or
b) Redisplay the original setting (e.g. This Firewall)

It will be something in the JavaScript which is doing different stuff for the dsttype field than for the srctype field.