Except that doesn't happen? In the night meetings the cop never has a verbal interaction with his/her suspects. Therefore interrogation never actually happens. (Unlike the Jailer or the Interrogator) Even if the cop gets N1'd and he/she investigates the mafia, the cop's investigation (or interrogation) has no impact on the game whatsoever. (Although in most cases whenever someone gets I'm Miller I Swear, it's usually because they cc'd cop and the guilty has no bearing on the situation)
this isnt a bug dude. this how it should be. cop found the mafia, but cop didnt live to tell. mafia claimed miller to cop. how do you think cop finds mafia? cop interrogates/investigates people at night. interrogation in this case, because they claim miller.