A bug, I would have to say yes & no. It seems if you ever take any kind of shell
or DC damage, your crew can repair most of the inside stuff but NOT the outside hull. There is a % (less than 100) of how much the hull is damaged. The lower the
%, the less deep you can dive. The ONLY way to get it fixed is to end the patrol
at the base you are assigned too. There is a damage analyzer someone made that
lets you know after a save just what the damage is. Look at this thread:
http://www.subsim.com/radioroom/showthread.php?t=114405
JIM