Zac ult goes on full CD after interruption

This has been a long-standing bug that Zac has, where if he presses ult, there is a short period of time (~.3 seconds) where his ult will not do the initial knockback. This occurs due to any displacement, death, or triggering of his passive, (not sure if non-displacement hard CC triggers it) leading to some awkward and frustrating situations. An example of this situation is Zac fleeing from an enemy, trying to ult to knock them back only for them to kill him right after he casts the ult, putting it on full cd. Similar ults such as Illaoi's which have brief delays after cast before the ult takes effect do not go on full cd if they are canceled. Fixing this bug would be a nice QOL/Bugfix to reduce frustration.