1d Mark IV Auto Focus Question

Take a look at the "AF point expansion" section of this Canon Document:

http://www.learn.usa.canon.com/resources/articles/2011/whats_new_eos1dmarkiv_auto_focus_article.shtml

It may be the way you have CF III 8-3 set:

" Here’s how it works: When C.Fn III-8-3 is combined with AI Servo AF, up to 18 AF points adjacent to the manually-selected AF point will become active. Each time the subject moves to another AF point, the expanded AF points will also shift to surround the AF point covering the subject. In response to the subject's movement, the AF point lit in red also shifts continuously. Since the clump of active focusing points can shift automatically according to subject movement, all 45 focusing points are effectively available for burst mode shooting."