I haven't seen any solid evidence that he wasn't born in Hawaii, but I did pre-order Corsi's book and am looking forward to reading it.
I think you are right and I think his parents were never legally married as Obama senior had a legitimate wife in Kenya. And Obama junior does not want to be a legitimate bastard.
If that is his problem which causes him to hide the certificate, with all the babies born to the unweds, he is overly sensitive. It is more a reflection on his mother not on him.