So, just played a game as Karthus, farmed up my tear to 500ish bonus mana then upgraded to the archangel staff while dead. Upon ressing, I noticed that the mana counter was back to 0 instead of the farmed amount while still retaining the bonus mana on my bars. I was not able to test to see if the staff could have granted 1000 mana since the game ended, but it should be looked at
Buy a tear of the goddess
Farm up to 500ish mana
While dead, buy the staff upgrade
So, yeah. Lets see if we can nail down what is causing this glitch or if it was a one time graphics bug.