Situation: Labyrinth, starting the fight with Rex. He has 82 attack damage, I am Orc Warlord with 98 hp, two layers of corrosion and a layer of death protection on me. Normally, I would survive a hit from him, but my positioning is horrible and whatever I'd do, he would knock me in a wall or petrified gorgon for additional damage. I attack him, expecting him to knock me back into a petrified gorgon and deal me 164 damage(as per Knockback 100% property) and therefore expend the level of death protection. The result is that the gorgon statue is smashed, and I am left at 1 hp, but the death protection is not expended. Combat prediction was telling me "safe".
This is either a bug with knockback and death protection, or Rex just dealing 95 damage, in which case I survive normally. If latter is true, then "Knockback 100%" does not make a whole lot of sense.
On a slightly unrelated note, when you hover over a monster which is a lower level than you while playing Assasin combat prediction always says "safe".
EDIT: Quest "Here Be Dragons" shows an empty reward.