I wonder if we should ban that in the validation - not let the user put the equivalent of an internal interface name (WAN, LAN, OPT1, OPT2…) for the description of another interface. It is a total recipe for confusion if someone puts OPT5, OPT2, OPT7, OPT1, LAN... randomly as the descriptions of LAN, OPT1, OPT2, OPT3, OPT4...

There is input validation there to prevent conflicting interface names on interfaces.php (so that conflict could only last until the interface is enabled). The only possibility for introducing problems there is if you can enable the same interface multiple times with the same name, which is prevented.

That's the type of validation that probably goes too far, in that someone surely would complain that they can't call their <opt1>interface OPT2 (or similar). Sure it's a bad idea, but if it's not going to hurt anything, let people do what they want.</opt1>

What you describe is not supposed to happen. Post screen shots of the Interface->(assign) screen, and Firewall Rules tabs that will show 2 "OPT1". And give any other clues about what is unusual about your system.

Attached. I don't have any other information as to what is usual