The Cayman Islands Flag? Really?

Last week was the first week of school, and I was in another dimension, so you guys may have already discussed this, but that flag really jumped out at me when Mitt's yacht was being talked about. I'm not sure as to the legalities...I figure it's a tax dodge in the first place, and he has to fly the Cayman Islands Flag as that's where he has it registered. Obviously, he wouldn't fly the American Flag under the Cayman Islands, but is there something that says he couldn't fly an American Flag on another, equally sized post?

Just asking...him being such a patriot and all.