TargetOpponentsChoicePermanent is buggy with hexproof

A judge confirmed me that cards that choose "target permanent of an opponent's choice" should be able to target hexproof permanents under the control of the effect's controller. This currently isn't the case.

**Example**: Cast Diaochan, Artful Beauty and equip her with Swiftfoot Boots. Unless there is another creature on the battlefield (in which case the opponent can only target that creature), her ability bugs out and doesn't activate due to "no valid targets" from the opponent's part of the ability (only you, as her controller, can pick her as the first target).

If it's of any note, the part where the chosen opponent can't pick his own hexproof creature as the target is implemented correctly.

Relevant link here: http://tappedout.net/mtg-questions/a-couple-questions-about-diaochan-artful-beauty/