When Black Knight and Aegir both have their specials activated, BK can mitigate damage to 1; however, Aegir then spreads out what I assume is the unmitigated damage to the surviving heroes.
What should happen: Black Knight receives 1 damage, all other heroes receive 0 (or 1).
What actually happens: Black Knight receives 1 damage, all other heroes receive 50 (or whatever that number would be if they were hit without Black Knight active.