Kassadin (Riftwalk bug)

Server:EUW Type of Bug:In-game Reproduction rate:10/10 In the link above there is an image that you can see the bug. The problem is that when you reach 45% cooldown reduction on kassadin and you also have the ultimate hat maxed (meaning you will have a total of 60% cooldown reduction on riftwalk) your riftwalk cooldown reduction on lvl 16+ is 0.94 seconds as you can see in the image, but it should be 0.8 seconds based on math since 2-0.6*2=0.8 seconds not 0.94 seconds. You can replicate the bug by making kassadin have 45% cdr and then max ultimate hat. In this image i used lich bane, ionian boots and zhonyas to get to 30%, transcendence to get to 40% at 10 min and cosmic insight to get to 45%, then i maxed ultimate hat by making 5 ultis.