When Kalista autos an enemy minion placing a spear in the minion and a support with targons goes to auto attack and execute the minion if teh execute damage is higher than the damage that teh support normal deals on hit the minion will die and gold awarded to only kalista with no stack being consumed from Targons
Basically Kalistas passive ability to stack the spears in what she auto attacks messes up the execute ability granted by Targons
I can't even understand your comment 
Just played a game of Leona + Kalista. It seems to be related to the distance you are from Kalista. Closer gets free executes (charge not consumed) giving gold only to Kalista. Further away Targons works normally. It also seemed like Targons worked normally with ranged creeps.
