Why is the ruling on this move being changed?

[tcarilli]

Originally Posted by jicecone

..."I think they should get rid of it," Yankees reliever Boone Logan said. "Us lefties can't do that. If we do, they call a balk."

Unless I am missing something, a left-handed pitcher can step toward third fake a throw there, disengage the rubber, and throw to first. Now it would look silly and I have never seen it. But there is no rule precluding a lefty from doing a third-to-first move.