manamune toggle

Yorick has this bug where if you die with your ult with manamune toggled on or off/or toggle it in your ghost it will visually show that it is on but theres no other real indication that it is working you wont lose mana from what ive seen damage doesnt go up and theres no way to reactivate it, its just permanently "on" ive had this happen twice, i play yorick do you even remember