If you have the Amulet of Immortal and you use the Resurrect spell when you died the chat shows that you discovered the Spell but if you look at the Spellbook or at the thing where it shows which spell you have selected it shows that you didnt discover it yet
i will edit this soon and write to it if in multiplayer when you use Resurrect on others if it works normal or not

Edit: After rejoining it shows that i discovered it