He did that when he gave the Oath of Office to a man he knew full well was ineligible. That's why the Freudian slip, where he mixed up the wording of the Oath and Obama himself said the correct order of the wording. Then Roberts had to administer the Oath again in chambers. Something is very, very wrong.
That was my initial thought as well. I believe Roberts’ decision has to do with the dirty little secret the share about Obama’s ineligibility.