[GAMEPLAY] Keystone "Press the Attack" resets upon landing an attack

Server: EUW

Type of Bug: In Game bug

Description: Keystone "Press the attack" : the amount of stacks on the target resets upon landing a basic attack (or a spell that behaves like a basic attack) which means you have to attack 4 or 5 times to activate the effect. I first experienced this with Ezreal : after landing two basic attacks, I landed my Q and the rune didn't activate, instead my target had only one stack left. That makes 4 basic attacks and a Q to activate the rune. It also occurs with Draven : landing two basic attacks only built one stack. That makes 4 basic attacks to activate the rune. Lastly, it occured with Jinx : target had two stacks, third basic attack brought the amount down to one. That makes 5 basic attacks to activate the rune. Also note that it happens very rarely but can almost always be reproduced the first time you attack a champion in a game. This bug most likely happens on other champions (for example Jax and Gangplank) however I was not always able to reproduce it as easily as I did with the three above.

Video / Screenshot: The three examples above recreated with the practice tool. https://youtu.be/OM9LvVgYDqw

Steps to reproduce: Select "Press the attack" as your keystone rune and use basic attacks (and spells that behave like basic attacks) against a target in order to activate it.

Expected result: "Press the attack" : Basic attacks against enemy champions apply stacks for 4 seconds. Applying three stacks activates the rune, dealing bonus damage.

Observed result: The amount of stacks resets upon landing a basic attack (or spell) on the target which means you need up to 5 attacks to activate the rune.

Reproduction rate: 8 out of 10 times on the very first try on an enemy champion. Almost never occurs after.

System specs: Windows 10/GTX950m/6GB RAM/i5 processor