Serious Zed Ult bug (WITH 100% REPRODUCTION RATE!)

This bug is actually a long-standing one, but only recently did someone find a video of it.

100% reproducible.

Video: https://gyazo.com/70fdb844564444e217d5c7874add2b06

Description: After QSSing Cho'Gath's knockup, and immediately ulting on Cho'Gath, Zed is somehow able to ignore the delay on his R's backswap. He's able to use it immediately. Additionally, the Q spell - Razor Shuriken - cannot be used for a moderate degree of time (3-10 seconds) regardless of its cooldown status. Notice that Cho'Gath's silence is not being used at all.

In the clip, the key at the far left near the bottom of the screen is the most recent key that the player has pressed. It's an app built with Riot's API. You can see that he is using Q several times throughout the clip, without it being able to be cast even though it is not on cooldown.

How to replicate (with 100% accuracy):

Step 1. Have ANYONE knock you up or knock you back (it doesn't have to be Cho'Gath)

Step 2. Cleanse the knockup/knockback with QSS

Step 3. IMMEDIATELY use your ultimate after the cleanse

Step 4. Press R as soon as you reappear and you will see that you are able to swap-back immediately to your ultimate shadow, ignoring the built-in delay. Additionally, Q cannot be cast until long after Death Mark pops. The only spells Zed is able to use during this period of time are W and E.