Damage Not Showing?

[Bathrone]

Ok so my first mission in career mode I got into killing things in Tokyo harbour. 57000 tonnes sunk, and 5 aircraft. Actually it goes to show how lame the AI is when it comes to attacking ports...I mean at one point I even surfaced and started taking them out with my stern cannon. How ridiculous. But anyway I digress.............

So I got a fair whack of damage and repaired it all. I had no damage left that was visible for showing on the "Y" screen. When I got back to port I was busted by the brass for wrecking the sub, but since I did so well they gave me another one. This is confusing as I had no damage left??