They usually have you file for both ssdi and ssi when you first file. i wont say always because there are people here that are waiting to jump on anything you say and as im sure you have learned in life nothing is absolute. The reason to get the SSI money and then have to pay it back is because you may not qualify for ssdi after they check the non medical qualifications, but they is usually done very early. Also many people as you know are losing their homes, cant afford medicine etc so even if you have to pay back that money at least you have it if you are qualified for it.