Diamond Skin has another bug going on with it: Clicking (or pressing the button, for you trolling bastards who go "Click! OMFG PRESS BUTTON NOOB" when it's obviously implied to be either the latter due to ease of writing or both cases) will show the button onscreen depressing as if the skill is being activated but... then it won't activate. at all. You can even click it multiple times and not have it take effect- And this is the skill we can use even when stunned, so it's not a case of CC stopping us. There are videos on youtube that showcase similar issues.
Lastly, any spell that doesn't have a single hit (Arcane Orb, Magic Missile... pretty much it) does NOT apply on hit effects like %damage as life or on hit +life, or, most worryingly, does not apply Conduit, Venom, or Blood Magic runed Magic Weapon.