Arms Race map bug-nuclear bomber did not start a war

I attacked a AI city with a nuclear bomber (not declaring war first).

The in game report

5:32 pm South California: A Nuclear Bomber has been destroyed by the 10th SP Rocket Artillery Division (Oregon).

5:32 pm San Francisco: The 33rd Atomic Bomber Squadron (South California) (CJ 33) has been destroyed.

Casualties since the beginning of this war:

South California - 11,400

Oregon - none

Relations with AI are still No-Trade. In the past IT would be Nuclear strike, war declared....