Right after the Millennium Falcon shoots over the top of the Star Destroyer's bridge and then affixes to the back of the superstructure, there is understandably some serious consternation going on since that panel is not in view of any of the scanners. (Seriously, why didn't they have 100% coverage of the surface of their own ship?!) The crew immediately apprise Captain Needa of the situation and tell him they will continue searching, so why does the captain immediately announce that he will take full responsibility for the loss and then go to voluntarily apologize to Vader and submit himself to his mercy (or lack thereof)? Couldn't he have waited at least a little longer, especially since he almost certainly could have foreseen how Vader would react?
Remember, all this happened probably fewer than 12 hours after the Battle of Hoth and Vader's choking of Admiral Ozzel (from another part of the ship via tele-conference, no less!). I'm pretty sure that event was still quite fresh in officers' memory. Needa himself may even have watched it happen!