Run the attached repro mission.
You will start with a rating of -1990 always displayed in the hint.
Shoot Unit 1, your rating will drop below -5000, you lose command and unit 2 will attack you. Shoot Unit 2, rating will go down -8000 or something. As it should be.
Restart the mission, kill Unit 1 via the action menu, order "report status". As soon as you realize that he's down, your rating will be at -2090.
Immediately kill Unit 2 via action menu, request status, rating will stay at -2090.