I've mentioned a bug a while back and I'm writing a bug report to bring it up again, in the hope that it will get addressed at some point. It is not a small bug, for it skews all damage calculation and creates large balance issues.
So the bug is like this : as long as a ship has 1 defense remaining for a type of damage, this type of damage will not hurt HP. A ship with 1 shield can soak a 1 million-strong laser volley and only lose its 1 shield without loss of structural integrity. It's a bad bug because it seriously advantages small ships over large ones and can be easily exploited.