When an unconscious and bleeding player dies the body will do the fall animation - making it flop up from the ground and fall back down, and often change direction. Looks very weird, see the attached video.
I think previously the body would just change its position slightly from the unconscious aspect to the dead aspect, this "flop" is recent I think. Video captured in 1.11 but it still happens.
Also, bodies in stairs should be aligned with the staircase.