A minor bug that came up that I thought was squashed already.
When attacking an AAA gun alone with just air, the AA gun should not get to defend.
No Combat Value: Even though an AAA unit can defend, either alone or with other units, it has a combat value of 0. This means that an AAA unit cannot fire in the defending units fire step. It can, however, be taken as a casualty. If a territory containing AAA units and no combat units is attacked, the AAA units are automatically destroyed. AAA units may never attack.
and
Air Defense: An AAA unit can fire at an air unit only when that unit attacks land and/or air units in the territory containing that AAA unit.