Or maybe that was intended, since the Boss, and/or other NPCs, and/or MoBs might be "immune" to one or more skills which are currently equipped on the active ability bar. Or they might be "immune" to the type of damage inflicted by the weapon which your character has been using, and/or by its enchantment.Probably not attended, but while dead you able to change out skills even though group is in admist of combat. Only works on active bar though.