Strange Heads-Up Showdown Rule

Playing in a limit 7CS tourney, I learned that if two players have a showdown, both players always have to show hands, even if nobody is all-in. Is this a standard rule and if yes, does it apply only to tourneys and/or only to stud? (I understand, that any player in the hand has the right to see mucked cards upon request to prevent collusion, but the floorman stated that cards would always have to be shown.)


cu


Ignatius