Kalista - Rend does not stack

Was in an aram game as Kalista and rend does not stack up. Below is the game history. http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2058888133/47182176?tab=overview

Steps are easy but I don't know if this is common.

1. Pick Kalista
2. Start a game.
3. Level E
4. Auto a champion several times
5. Press E
6. See dmg dealt

I'll try this in a custom game once and see what happens.