Ezreal Q Cooldown Bug (Gameplay)

Hello, First of all I got to say that i have not any videos proofing this bug. Maybe somebody else can tell their experience they have probably made with Ezreal Q. Some minutes ago I've played Ezreal and while playing i figured out something is wrong about the Q. I was farming and spamming Q but sometimes It was taking longer to get off Cooldown. I tried a bit and my first theory was that when Ezreal is in meele range and hits the unit his Q doesn't get the 1,5 seconds Cooldown reduction. But sometimes he got his 1.5 seconds but i'd say like 60% of all Qs in range "50" didn't return this 1.5 second cooldown reduction. That's it.