Non, c'est pas ça: j'ai trouvé ce qui va pas sur uesp.net :
When any quest items (i.e., items that normally cannot be dropped from your inventory) that are equipped are forcibly removed from your inventory, the game removes the item but does not remove the item's magical effects. Therefore, you end up with a permanent magical effect. This effect is truly permanent: there is no way other than Console commands to get rid of it. There may be undesired side effects from having permanent effects.
The quest items cannot be equipped ("You cannot equip this enchanted item right now.") or dropped ("You cannot remove Quest items from your inventory."), but their effects remain.
Apparement, le seul moyen de résoudre mon prob c'est une ligne de commande dans la console... Je sais pas si qqn s'y connait dans ce domaine?