I’ve reported this like 2 months ago and still not fixed. When soldiers on stairs detect enemy units, they die out of hart attack. Straight on the spot.
My soldiers just take 2-5 damage, but I encounter this bug only on 45 degree stairs.
Stairs ? 
Yesterday I’ve got an instadeath on hopping over a flat table and on the same map a Triton also dies as he jumps over another relativly flat obstacle.
So, I confirm the bug and it seams to be on both sides and on different obstacles not only stairs.