When I reached Calculator's Lair it appeared that General Barnaky, all the brains and Calculator itself where invisible - see screenshots. It was not possible to interact with them by any means other than damaging them with explosives or browning. Barnaky was also not active in battle, just standing still. As no talking possible, the only ending I could get was one with destroying Calculator.

I played this game through Wine in Linux which possibly is the cause, however still very strange as I played whole game and didn't encounter a single technical issue before. Can't even think why could such thing happened.