Title incorrect, I now know that the bug occurs independent of Karthus dying.
EDIT3: I reproduced the bug doing almost exactly the same thing in both games (as outlined below), occurred at the exact same time (Killing Blue buff) I'll attempt to repeat this bug with a different champ now.
EDIT2: Video of the bug in action: http://youtu.be/Mqhxjko0940, I have to keep moving my mouse over the tooltip to update it. You need to watch the video in HD to read the tooltip.
EDIT: Tried to reproduce this bug by buying Eleisa's immediately and dying at 2 stacks, did not reset this time. Will upload a video replay of the game where it was happening.
I'll also try reproducing this bug by doing exactly what I did the first game, which was:
Play Karthus, Buy level 1 boots and pots
Save till philo stone, recall and buy
Save till Eleisas and Sorcs Shoes with Homeguard
Gain 1 Level
Fight blue buff.
Quote:This has happened to me before on Sona, and many others in another thread (http://na.leagueoflegends.com/board/....php?t=2820658)
I've tried my best to remember what happened in said match, but cannot remember any one thing that might have made it bug (that I haven't tested already, like moving the item in inventory to another slot, using specific actives, reviving, dying, opening shop with alive/dead). In solo custom's I have not been able to reproduce it yet. If you have any more info, or have a link to a video please post it.