Is this a surprise? Perk is a liability on offense when he is anything more than a 5th option. If all you ask him to do is swing the ball at the top of the key, finish wide open layups, pound the boards, and make the occasional low-post move to keep defenses honest, then he is effective. When you expect him to be a more integral part of the offense, then all of a sudden he becomes a liability. That is not going to change.
Really, I think someone needs to sit Perk down, and tell him that he needs to back off a little and just do what he does best. I think he has been trying to take it upon himself to do more when KG is out, and it has become detrimental to the team. Get him back into his comfort-zone as a defender and last option on offense, and it will go a long way to improve things.