Could be related to a juicy scenario Jerry Corsi posited a week or so ago? Grandma Toots was only 38 years old when BO was born. She was quite attractive. Marshall Davis told of an affair with a married white couple in one of his porn novelettes. Corsi claims to have some evidence that the frequent moves by Stanley and Toots may have been related to indiscretions involving Toots. There are apparently photos of Ann on the beach a few months before the birthdate looking typically svelte - as the salacious nude photos, which I of course have never seen, supposedly show. Toots, Corsi claimed, like Ann, as described in Dreams from my Father, was very attracted to black men.
This, of course, just adds to the confusion, but may offer some more reasons for the concealed birth certificate. If Toots, who raised BO, were the birth mother, Davis was a bit old to be the father, but Obama senior wasn't.