Attrition + race bonus = units left "problem"?

So I've observed strange thing which undermines race bonuses a bit. From what I'm aware of, in case of draw in rolls on attrition both regions should be left with 1 unit. This is not true in case of bonused rolls. I've just seen 7 Vampires attacking 8 Demon with result of 27:27. Demons were left with 2 units. Also I've seen it before with pumpkins but didn't pay so much of attention. In fights 8v8 dice with results similar to 26:27 enemy was left with 3 (!) units. I suppose it should be 2 if not 1? Or am I mussing something?
Please correct if me I'm wrong but it seems like units left in the region after fight are based on main roll value without bonus?
Please correct if me I'm wrong but it seems like units left in the region after fight are based on main roll value without bonus?