So playing as Leona today with Kalista I ran into a problem. Her passive gives bonus damage when I attack a mob she just recently attacked. Now this is great in most cases but when I'm trying to use up a charge of the 
or any upgraded form of that item the bonus damage counts as a kill for Kalista. This makes it pretty difficult to use up the charges on the item and there for making the sharing of gold much harder. 
I've been noticing this as well. While not "Game-Breaking" per se, it is very annoying as it makes it tricky to use the Charge consistently on the cannon minions.
Yeah, it's really annoying and it makes it close to impossible to use the item. I had to resort to telling my adc (via voice chat) to not hit a specific minion so I can take it. Or time my hit while there is no mark on the minion. Late game when kalista has a lot of Attack Speed, she marks faster than I can hit a minion soooo no gold for me even out of lane phase.
And the dumbest thing is that kalista feels like she should be used with supports that use Targon's Brace ... cmon Riot this should have been fixed in beta
Oh that reminds me I think in one or two games while playing with Targon's brace I did not see Kalista minion markers ... maybe a bug, maybe I'm mistaken.
