[GAMEPLAY] The Black Cleaver not granting 20% CDR

Picture for those who can't access the link is provided somewhere below (I hope)

TLDR; Bought Black Cleaver, got 10% CDR instead of 20% CDR Reproduction rate: 1/1 (Going in game 2 to test now) Expected result: Gain 20% cdr. Observed result: only 10% CDR

I was playing BMB and using Miss Fortune when I felt that somewhere late into the game that my ultimate wasn't up as often as it should be. Checked it and I was right. I could have provided better proof by showing the individual cooldowns on the picture but when I checked my Q and R were 2.7s and 90s respectively, which basically hinted at a 10% instead of 20% CDR

EDIT:

Turns out it isn't a Black Cleaver bug.

It's a Mirage Blade bug.

With the last 2 screenshots I added in you can see that when I sell my Mirage Blade my 10% CDR disappears. Guess I found the source of the bug.